SEWERS  AND  DRAINS 


A  COMPREHENSIVE  DISCUSSION  OF    MODERN  SANITARY  METH- 

ODS  IN  THE  DESIGN  OF  SEWERS  AND  SEWERAGE  SYSTEMS, 

IN  THEIR  LAYING-OUT,  COST,  AND  CONSTRUCTION 

AND  IN  THE  DISPOSAL  OF  SEWAGE 


BY 

A.  MARSTON,  C.  E. 

DEAN  OF  DIVISION  OF  ENGINEERING  AND  PROFESSOR  OF  CIVIL,  ENGINEERING, 

IOWA  STATE  COLLEGE 

MEMBER,  AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS 
MEMBER,  WESTERN  SOCIETY  OF  CIVIL  ENGINEERS 


THOMAS  FLEMING,  JR.,  B.S.,  C.E. 

WITH  CHESTER  AND  FLEMING,  HYDRAULIC  AND  SANITARY  ENGINEERS 

ASSOCIATE  MEMBER,  AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS 

MEMBER,  NEW  ENGLAND  WATER  WORKS  ASSOCIATION 

MEMBER,  ENGINEERS'  SOCIETY  OF  PENNSYLVANIA 


ILLUSTRATED 


AMERICAN  TECHNICAL  SOCIETY 

CHICAGO 

1917 


COPYRIGHT,  1908,   1917,  BY 

AMERICAN  TECHNICAL  SOCIETY 


COPYRIGHTED  IN  GREAT  BRITAIN- 
ALL  BIGHTS  RESERVED 


INTRODUCTION 

TN  these  days  of  complex  living,  the  health  of  the  public 
is  an  all-important  factor  which  must  be  considered 
in  all  its  phases.  In  olden  days  more  serious  infections 
and  prolonged  epidemics  were  brought  about  by  careless 
sanitation  than  by  almost  any  other  cause.  The  germ 
theory  of  disease  was  not  then  understood  and  hence  the 
inhabitants,  blissfully  ignorant  of  their  crime,  were  con- 
stantly doing  all  sorts  of  fearful  things  and  daily  breaking 
all  of  the  now  well-established  laws  of  sanitation  and  public 
health.  Thanks  to  the  efforts  of  scientists  we  now  know 
just  what  must  be  done  with  our  water,  our  sewage,  and 
our  garbage  in  order  to  avoid  typhoid  and  other  serious 
epidemics. 

9  The  authors  of  this  article  have,  by  long  service  in  the 
academic  and  practical  fields,  qualified  themselves  to 
speak  with  authority  on  this  subject.  They  have  given 
a  great  deal  of  practical  information  in  the  design  of 
sewers,  systems  of  sewerage,  sewage  disposal,  layouts, 
typical  specifications,  sewer  materials,  tables  and  diagrams 
for  calculating  sizes,  capacities,  and  costs  of  construction. 
Altogether  the  treatise  will  be  found  very  interesting  to  the 
layman  and  extremely  valuable  for  the  practical  man 
engaged  in  sewer  work. 


CONTENTS 

DESIGN  AND  CONSTRUCTION  OF  SEWERS 

PAGK 

Systems  of  sewerage 7 

Water-carriage  systems 10 

Combined  system 10 

Separate  system .  •  •  •  • 10 

Comparative  merits  of  combined  and  separate  systems. . . 11 

General  features  of  sewers 13 

Kinds  of  sewers. 13 

General  description  of  sewers 15 

Location  of  sewers 16 

Streets  vs.  alleys  for  sanitary  sewers 17 

Depth  of  sewers 18 

Subdrains. 19 

House  connections 20 

Manholes 21 

Lamp  holes 23 

Flush-tanks 23 

Automatic  flushing  siphons 26 

Hand-flushing  of  sewers 28 

Sewer  ventilation 28 

Street  inlets  and  catch-basins 29 

Inverted  siphons 30 

Outlets  for  sewer  systems 32 

Sewage  disposal 33 

Sewer  materials  and  cross-sections 33 

Sewer  materials 33 

Joints  in  pipe  sewers 36 

Cement  sewer-pipe 37 

Typical  cross-sections  of  large  sewers 39 

Junction-chambers  for  large  sewers 40 

Brick  sewers 41 

Concrete  sewers. . 42 

Formulas  and  diagrams  for  computing  flow  in  sewers 43 

Formulas  for  computing  flow  in  sewers 43 

Diagram  of  discharges  and  velocities  of  circular  pipe  sewers  flowing  full .  45 
Diagram  of  discharges  and  velocities  of  egg-shaped  brick  and  concrete 

sewers  flowing  full 49 

Diagram  of  discharges  and  velocities  in  circular  sewera  at  different  depths 

of  flow 52 

Diagram  of  discharges  and  velocities  in  egg-shaped  sewers  at  different 

depths  of  flow 54 

Summary  of  laws  of  flow  in  sewers 57 

Calculations  of  sizes  and  minimum  grades  of  separate  sanitary  sewers 58 

Minimum  sizes  of  sanitary  sewers 58 

Minimum  grades  and  velocities  for  separate  sanitary  sewers 59 

General  explanation  of  the  calculation  of  amount  of  sanitary  sewage.  ...  60 

Methods  of  estimating  the  population  tributary  to  sanitary  sewers 61 

Use  of  statistics  of  water  consumption  in  determining  the  per  capita  flow 

of  sanitary  sewage 62 


CONTENTS 

Calculations  of  sizes,  etc.,  (continued)  PAGE 

Capacities  of  sanitary  sewers  required  to  provide  for  fluctuations  in  the 

rate  of  flow 64 

Ground  water  in  sanitary  sewers 66 

Summary  of  methods  of  computing  sizes  of  separate  sanitary  sewers.  ...   67 
Table  of  sizes  required  for  sanitary  sewers 69 

Calculation  of  sizes  and  minimum  grades  of  storm  and  combined  sewers. ...  71 

Storm  and  combined  sewers  calculated  by  same  methods 71 

Minimum  sizes  of  storm  and  combined  sewers 71 

Minimum  grades  and  velocities  for  storm  and  combined  sewers 71 

General  explanation  of  the  calculation  of  amount  of  storm  sewage 72 

Calculation  of  the  time  of  concentration 74 

Calculation  of  the  rate  of  rainfall  corresponding  to  the  time  of  concen- 
tration   75 

Calculation  of  the  percentages  of  impervious  and  pervious  areas  on  the 

sewer  watershed 76 

Calculation  of  the  maximum  percentage  of  run-off 79 

Summary  of  methods  of  computing  sizes  of  storm  sewers 80 

DRAINS 

Land  drains  and  subdrains 83 

General  discussion  of  land  drains 83 

Planning  and  construction  of  land-drainage  systems 83 

Contracts  and  specifications  for  tile  drains 84 

Benefits  of  tile  drains 86 

Benefits  of  large  ditches 87 

Method  of  computing  sizes  of  tile  drains 88 

Method  of  computing  sizes  of  drainage  ditches 89 

Method  of  computing  sizes  of  subdrains  for  sewers 89 

Cost  of  tile  land  drains  and  drainage  ditches 92 

HOUSE  SEWERAGE 
General  Principles 

House  sewers 94 

House  plumbing 95 

Soil  pipes 95 

Traps 96 

Ventilation 96 

Cost  of  sewers,  and  methods  of  paying  for  them 96 

Preliminary  estimates  of  cost  of  sewers 96 

Cost  of  pipe  sewers 97 

Cost  of  brick  sewers 99 

Cost  of  manholes,  combined  manholes  and  flush-tanks,  flush-tanks,  etc. .  103 

Engineering  and  contingencies 103 

Methods  of  paying  for  sewers 104 

SPECIFICATIONS  FOR  SEWERAGE  SYSTEMS 

Preparation  of  plans 105 

Sewer  reconnaissance 105 

Surveys  for  sewer  plans 107 

Sewerage  plans 109 

Specifications  for  sewers Ill 

Form  for  sewerage  contract 123 

Form  of  bond  for  sewerage  contract 124 


CONTENTS 

CONSTRUCTION  AND  MAINTENANCE  OF  SEWERS 

Construction 125 

Letting  the  sewer  contract 125 

Organization  of  construction  force 126 

Laying  out  the  sewer  work 126 

Trenching  and  refilling 127 

Sheathing 128 

Pipe-laying 129 

Construction  of  brick  sewers 129 

Records  of  sewer  construction 130 

Maintenance 132 

Sewerage  systems  should  be  carefully  maintained  in  good  condition 132 

Sewer  ordinances,  permits,  and  records 132 

Plumbing  regulations,  tests,  and  licenses 132 

Flushing  and  cleaning  of  sewers.  . 133 

Cleaning  of  catch-basins 134 

SEWAGE  DISPOSAL 

Sewage 136 

Character  of  sewage 136 

Analyses  of  sewage 136 

Disposal  systems 140 

Requirements  of  sewage  disposal 140 

Classification  of  methods „ 140 

Controlling  factors 140 

Dilution  of  Chicago  sewage 141 

Efficiency  of  broad  irrigation 142 

Efficiency  of  chemical  precipitation 143 

Coarse  screens 144 

Fine  screens 144 

Settling  vs.  septic  tanks 148 

Polk  tanks 152 

Two-story  tanks 155 

Greenville  tanks 159 

Radial-flow  tanks 161 

Sprinkling  filters 166 

Use .166 

Design 166 

Polk  niters 170 

Summary 184 

Sewage-disposal  method — question  of  conditions 184 

Care  of  suspended  matter  and  effluent 184 

Disinfection  of  effluent 184 

Future  conditions 185 

GARBAGE  DISPOSAL 

General  features 185 

Composition  of  garbage 185 

Quantity -.186 

Disposal 186 

Collection 186 

Incinerators 186 

Requirements 186 

Design 187 

Reduction  plants 187 

General  conditions 187 

Columbus  reduction  plant 188 


AUSTIN  TRENCHING  MACHINE  DIGGING  TRENCH  18  FEET  DEEP  AND 
40  INCHES  WIDE 

Courtesy  of  Municipal  Engineering  and  Contracting  Company,  Chicago 


SEWERS  AND   DRAINS 

PART  I 


1.  Introductory  Definitions  and  Discussions.  Sanitary  Engineer- 
ing is  that  branch  of  engineering  which  has  to  do  with  constructions 
affecting  health.  It  thus  might  be  claimed  to  include  the  manu- 
facture and  transportation  of  foods,  the  architecture  of  buildings,  and 
many  other  things  which  affect  the  health  of  communities;  but  in 
ordinary  use,  a  more  restricted  definition  of  the  term  is  adopted. 

In  common  practice,  the  term  Sanitary  Engineering  is  taken  to 
include  only  water  supply  engineering  and  sewerage  engineering, 
the  former  branch  dealing  with  securing  a  satisfactory  supply  of 
water,  and  the  latter  with  the  satisfactory  removal  of  surplus  and 
waste  liquids.  Sewerage  is  the  subject  of  this  instruction  paper, 
water  supply  being  treated  by  itself. 

Sometimes  sanitary  engineering  is  given  a  still  more  restricted 
meaning,  and  is  taken  to  include  sewerage  only. 

A  drain  is  a  canal,  pipe,  or  other  channel  for  the  gradual  removal 
of  liquids.  In  sanitary  engineering,  the  two  principal  kinds  of  drains 
are,  first,  those  for  the  removal  of  comparatively  pure  ground  waters 
and  surface  waters,  as  in  land  drainage;  and,  second,  those  for  the 
removal  of  polluted  liquids,  as  in  sewerage  systems. 

A  sewer  is  a  drain  for  the  removal  of  foul,  waste  liquids.  Usually 
sewers  are  closed,  underground  conduits.  An  open  sewer  is  an  open 
channel  which  conveys  foul,  waste  liquids. 

Sewerage  is  a  general  term  referring  to  the  entire  system  of 
sewers,  together  with  any  accessories,  such  as  pumping  plants,  purifi- 
cation works,  etc.  Thus  we  may  speak  of  the  "sewerage"  of  a  city, 
or  of  the  "system  of  sewerage/'  or  of  the  "sewerage  system." 

Sewage  is  any  foul,  waste  liquid. 

Sanitary  sewage  is  the  foul  wastes  of  human  or  animal  origin 
from  residences,  stables,  stores,  public  buildings,  and  other  places  of 
human  or  animal  abode.  By  far  the  greater  part  (usually  99 . 8  per 
cent  or  more)  of  sanitary  sewage,  commonly,  is  ordinary  water,  which 


2  SEWEl^    VXD  DRAINS 

is  added  to/ijie;  Wastes  thejjnselyes  in*  this  large  volume  simply  to 
facilitate  removal. 

Manufacturing  sewage  is  the  foul  wastes  from  factories.  In 
different  factories,  it  is  of  extremely  different  nature.  It  is  often 
exceedingly  strong,  and  very  offensive  and  difficult  to  dispose  of,  as 
compared  with  sanitary  sewage. 

Storm  sewage  is  the  storm  water  flowing  from  city  surfaces  during 
and  after  rainstcrms.  Though  polluted,  especially  at  the  beginning 
of  a  storm,  from  the  droppings  of  animals  and  the  other  surface 
filth  of  cities,  it  is  not  so  foul,  nor  so  liable  to  swarm  with  disease  germs, 
as  is  sanitary  sewage. 

The  terms  sewage  and  sewerage  are  often  misused  by  persons  not 
engineers,  to  mean  the  same  thing.  Thus  such  persons  often  speak  of 
the  "sewage  system"  instead  of  the  "sewerage  system;"  of  the  "disposal 
of  the  sewerage"  instead  of  the  "disposal  of  the  sewage/'  of  a  city. 
So  common  is  the  misuse  that  some  sanction  can  be  found  in  the 
dictionaries;  but  engineers  should  be  careful  to  restrict  the  meaning 
of  the  word  "sewage"  to  the  liquid  which  flows  in  the  sewers,  while  the 
word  "sewerage"  should  never  be  so  applied. 

Sewer  air,  often  miscalled  sewer  gas,  is  the  air  in  the  sewers 
above  the  liquid  contents.  It  has  no  definite  chemical  composition, 
but  contains  varying  proportions  of  pure  air  and  of  carbonic  acid  gas, 
marsh  gas,  sulphuretted  hydrogen,  and  the  various  products  of 
decaying  organic  matter.  Sewer  air  is  constantly  changing  in  com- 
position even  in  the  same  sewer.  While  considered  injurious  to 
health  when  breathed,  it  has  not  been  proved  to  be  in  itself  the  direct 
means  of  communicating  infectious  diseases. 

2.  Historical  Review.  Sewers  and  drains  are  of  very  early 
origin.  Among  the  ruins  of  all  ancient  civilizations,  are  found  the 
remains  of  masonry  and  tile  conduits  constructed  for  drainage  pur- 
poses. 

In  Fig.  1,  for  example,  (from  Fergusson's  History  of  Architecture), 
are  shown  the  remains  of  a  large  masonry  sewer  or  drain  built  by  the 
ancient  Assyrians  in  the  eighth  or  ninth  century  B.  C.,  for  one  of  their 
palaces  at  Nimrud.  This  is  one  of  the  earliest  examples  found  of  the 
use  of  the  arch  in  masonry. 

In  Fig.  2  is  shown  the  mouth  of  the  Cloaca  Maxima,  or  great 
sewer,  of  ancient  Rome,  built  in  the  seventh  century  B.  C.,  and  stiii 


SEWERS  AND  DRAINS  3 

in  use  after  the  lapse  of  2,500  years.     Without  this  sewer,  a  large 
tract  of  ancient  Rome  could  not  have  been  inhabited;  and  in  speaking 


Fig.  1.    Ancient  Assyrian  Sewers  at  Nimrud. 

of  it,  one  authority  says:  "To  this  gigantic  work,  admired  even   in 
the  time  of  the  magnificent  Roman  Empire,  is  undoubtedly  owing  the 


Fig.  2.    Mouth  of  the  Cloaca  Maxima,  or  Great  Sewer,  of  Ancient  Kome. 

preservation  of  the  Eternal  City,  which  it  has  secured  from  the  swamp- 
ing that  has  befallen  its  neighboring  plains." 


4  SEWERS  AND  DRAINS 

In  many  other  ancient  cities  and  structures,  the  remains  of 
intelligently  planned  drainage  systems  have  been  discovered;  and  it 
is  evident  that  the  ancients  paid  great  attention  to  this  matter  so 
vitally  affecting  health.  The  art  reached  its  highest  ancient  develop- 
ment in  the  time  of  the  Roman  Empire.  The  Romans,  in  fact,  were 
the  greatest  engineers  of  antiquity,  and  especially  excelled  in  sanitary 
engineering  (both  water  supply  and  drainage).  They  were  pro- 
ficient in  land  drainage,  as  well  as  in  sewerage. 

With  the  fall  of  the  Roman  Empire,  sanitary  engineering  suffered 
the  same  retrogression  which  befell  learning  and  science;  and  for  a 
thousand  years — throughout  the  Middle  or  Dark  Ages — it  was 
almost  entirely  neglected.  The  impure  water  supplies  and  the  accu- 
mulated filth  of  mediaeval  cities  produced  fearful  consequences  in 
the  terrible  pestilences  which  desolated  Europe. 

With  the  revival  of  learning  and  science  in  the  14th  and  15th 
centuries,  attention  again  came  to  be  paid  to  sanitary  engineering; 
but  for  three  or  four  hundred  years  more,  little  was  done  toward 
putting  drainage  and  water  supply  on  a  scientific  basis.  Drains, 
rather  than  sewers,  were  built  in  the  various  towns  as  absolute  neces- 
sity made  imperative;  but  they  were  constructed  piecemeal,  and  not 
so  as  to  form  comprehensive  systems.  They  were  not  made  water- 
tight or  self-cleaning;  but  it  was  usually  considered  necessary  to 
make  them  large  enough  for  men  to  enter  to  remove  the  filth,  whose 
accumulation  and  festering  in  them  were  believed  unavoidable. 

In  England,  modern  sanitary  engineering  may  almost  be  said 
to  have  had  its  origin;  yet  so  late  as  1815,  laws  were  enforced  for- 
bidding the  emptying  of  faecal  matter  into  the  sewers.  "Such  matter 
was  generally  allowed  to  accumulate  in  cess-pools,  either  under  the 
habitations  of  the  people  or  in  close  proximity  thereto."  *  In  fact, 
though  no  longer  enforced,  these  laws  were  not  repealed  until  1847, 
when  Parliament  passed  an  exactly  contrary  act,  making  it  compulsory 
to  pass  faecal  and  other  similar  foul  matter  into  the  sewers. 

Modern  sanitary  engineering,  especially  as  regards  sewerage 
and  drainage,  has  had  almost  its  entire  development  since  1850.  It 
was  not  until  1873  that  there  was  published  a  comprehensive  treatise 
on  sewerage,  that  of  Baldwin  Latham,  already  quoted.  At  about 
this  time,  also,  much  attention  began  to  be  paid  in  England  to  sewage 


"Baldwin  Latham. 


SEWERS  AND  DRAINS  5 

purification.  It  was  reserved,  however,  for  America  to  put  sewage 
purification  on  the  road  to  a  satisfactory  scientific  solution,  by  the 
thorough  investigations  of  the  Massachusetts  State  Board  of  Health, 
begun  in  1887  and  still  under  way. 

In  America,  much  was  done  in  the  third  quarter  of  the  19th 
century  to  advance  sewerage  engineering,  through  the  studies  of  able 
engineers  in  connection  with  the  design  of  systems  for  Chicago, 
Brooklyn,  and  other  large  American  cities,  the  results  being  published 
in  papers  and  reports,  or  in  book  form. 

About  1880  the  separate  system  of  sewerage  came  strongly  into 
prominence  in  America,  as  advocated  by  the  late  Col.  Geo.  E.  Waring; 
and  the  construction  of  the  Memphis  (Tenn.)  sewers  on  this  system 
at  that  time,  together  with  their  great  success  in  putting  a  stop  to  the 
fearful  epidemics  which  had  so  often  desolated  that  city,  did  much  to 
make  sewerage  possible  for  small  cities.  At  present,  sewers  have 
become  so  common  and  so  necessary  in  modern  life,  that  villages  of 
2,000  population,  or  sometimes  of  even  less,  are  very  generally  taking 
up  their  construction. 

With  the  present  wide  adoption  of  sewers,  even  by  small  com- 
munities, sewage  disposal  has  come  to  be  of  very  great  importance, 
and  is  now  undergoing  great  development.  Many  discoveries  remain 
to  be  made  in  this  line,  in  which  the  guiding  principles  have  not  yet 
been  so  thoroughly  worked  out  as  in  the  construction  and  mainte- 
nance of  sewers  themselves. 

3.  Importance  and  Value  of  Sewerage  and  Drainage.  The 
importance  and  value  of  the  constructions  of  sanitary  engineering  can 
hardly  be  exaggerated.  Upon  them  absolutely  depends  the  health 
of  every  city.  One  needs  but  to  read  descriptions  of  the  great  modern 
epidemics  of  yellow  fever  at  Memphis  and  New  Orleans,  or  of  cholera 
at  Hamburg,  or  to  have  been  engaged  to  visit  as  sanitary  engineer  an 
American  town  during  one  of  the  numerous  recent  outbreaks  of 
typhoid,  to  understand  the  truth  of  the  scripture,  "All  that  a  man  hath 
will  he  give  for  his  life."  Yet  not  only  could  sanitary  engineering 
absolutely  prevent  every  such  epidemic;  but,  in  addition,  it  could 
annually  save  thousands  upon  thousands  of  other  lives  which  now 
succumb  to  bad  sanitation. 

Already  very  much  has  been  accomplished  in  this  direction  by 
improved  sanitation,  though  ideal  conditions  are  yet.  seldom  attained. 


6  SEWERS  AND  DRAINS 

A  prominent  sanitary  engineer  estimated  from  actual  statistics,  that 
as  early  as  1885  there  was  a  saving  from  this  cause  of  100,000  lives  and 
2,000,000  cases  of  sickness,  annually,  in  Great  Britain,  in  a  total 
population  of  only  30,000,000.  Figuring  on  the  basis  of  the  money 
value  alone  of  the  lives  saved,  and  of  the  sickness  and  loss  of  time 
avoided,  the  money  value  of  the  above  result  would  be  almost  incal- 
culable. 

In  many  individual  cities,  statistics  have  shown  in  death  rates 
an  immediate  lowering,  due  to  the  construction  of  sanitary  improve- 
ments, more  than  sufficient  in  money  value  to  the  community  to  pay 
for  the  entire  cost.  Funeral  and  sickness  expenses  saved,  alone, 
often  make  enormous  sums. 

In  this  connection,  it  should  be  said  that  pure  water  supply  and 
good  sewerage  are  both  essential,  and  that  it  is  impossible  to  separate 
the  value  of  one  from  that  of  the  other.  A  polluted  water  supply 
may  spread  disease,  no  matter  how  perfect  the  sewerage,  and  an 
abundant  water  supply  is  essential  to  the  proper  working  of  sewers. 
On  the  other  hand,  without  sewers  and  drains,  an  abundant  water 
supply  serves  as  a  vehicle  to  enable  unmentionable  filth  to  saturate 
more  deeply  and  more  completely  the  soil  under  a  city.  Cesspools  are 
even  more  dangerous  than  privy  vaults. 

In  addition  to  direct  prevention  of  communication  of  disease  by 
unsanitary  conditions,  modern  sewerage  facilities  are  so  great  a  con- 
venience that  this  advantage  alone  is  usually  more  than  worth  the  cost. 
This  is  shown  by  the  increased  selling  and  rental  value  of  premises 
supplied  with  sewerage  facilities.  No  sooner  is  a  partial  or  complete 
sewer  system  constructed  in  a  town,  than  prospective  buyers  or  renters 
begin  to  discriminate  severely  against  property  not  supplied  with 
modern  sanitary  conveniences;  and  persons  looking  for  new  locations 
for  business  ventures  or  residence  purposes,  discriminate  in  like 
manner  in  favor  of  towns  having  good  sewerage. 

So  great  has  become  the  demand  for  sanitary  conveniences, 
that  they  are  now  being  installed  in  farmhouses  as  well  as  in  the  city, 
It  is  now  possible  for  any  farmer,  at  an  expense  of  only  a  few  hundred 
dollars,  to  have  hot  and  cold  water  piped  under  pressure  in  his  house, 
a  bathroom  and  other  plumbing  fixtures,  and  his  own  sewage -disposal 
plant.  This  has  already  been  accomplished  in  many  cases.  Such 
improvements,  if  made  in  accordance  with  correct  principles,  greatly 


SEWERS  AND  DRAINS  7 

better  the  sanitary  conditions  of  the  home;  and  they  also  prevent 
much  disease  by  doing  away  with  the  exposure  to  inclement  weather, 
which  is  so  dangerous  an  accompaniment  of  the  old-fashioned,  bar- 
barous, outdoor  privy. 

The  great  importance  of  sewerage  may  be  realized  by  giving 
some  consideration  to  the  enormous  sums  of  money  which  have 
already  been  spent  for  sewer  systems  in  this  country  alone.  Villages 
of  3,000  population  in  rural  communities,  often  spend  $50,000  or 
more  upon  a  system.  The  city  of  Chicago  has  in  recent  years  spent 
$50,000,000  in  securing  merely  a  satisfactory  outlet  for  its  sewers, 
without  counting  a  dollar  of  the  vast  sums  expended  on  the  sewers 
themselves.  In  the  United  States,  hundreds  upon  hundreds  of 
millions  of  dollars  have  been  invested  in  sewers. 

SYSTEMS  OF  SEWERAGE 

4.  A  privy  vault  is  a  receptacle,  usually  a  mere  excavation  in 
the  ground,  for  the  reception  of  fsecal  matter  and  urine.  To  prevent 
dangerous  pollution  of  the  surrounding  soil  and  ground  water,  privy 
vaults  should  be  lined  with  water-tight  masonry;  but  this  is  seldom 
attempted,  and  even  if  attempted,  is  still  more  seldom  accomplished, 
for  it  is  difficult  in  such  work  to  secure  absolute  freedom  from  leakage. 
The  privy  vault,  frequently,  is  simply  abandoned  and  covered  over 
with  earth  when  full,  it  being  cheaper  to  change  the  location  than  to 
clean  out  the  old  pit. 

The  privy  vault,  with  its  inevitable  befouling,  in  the  immediate 
vicinity  of  the  home,  of  earth,  air,  and  water,  the  three  great  requisites 
of  health,  and  with  its  danger  from  pneumonia  and  other  diseases 
which  may  be  contracted  from  exposure,  should  be  adopted  only  in 
case  of  absolute  impossibility  to  secure  something  better,  and  even 
then  only  as  a  temporary  resort.  It  is  not  so  objectionable  in  the 
country  as  in  the  city,  if  located  far  away  from  the  well ;  but  here  the 
trouble  is  that  it  is  usually  placed  too  close  to  the  well  which  furnishes 
the  drinking  water.  In  the  country  the  teachings  from  hog  pens, 
cattle  yards,  and  manure  piles  frequently  add  to  the  contamination 
of  the  drinking  water.  It  is  impossible  to  set  any  safe  distance  at 
which  a  well  may  be  placed  from  a  privy,  owing  to  the  variable  nature 
of  the  soil.  The  contamination  may  be  carried  very  far  in  gravel 


8  SEWERS  AND  DRAINS- 

strata  or  rock  crevices.  Impervious  clay  confines  filtration  within 
narrower  limits. 

5.  A  cesspool  is  a  receptacle  for  receiving  and  storing  liquid 
sewage.  It  consists  usually  of  an  excavation  dug  in  the  ground,  lined 
with  masonry,  and  covered,  into  which  the  sewer  from  the  house 
discharges.  To  prevent  contamination  of  the  surrounding  soil  and 
ground  water,  the  cesspool  should  be  made  absolutely  water-tight,  and 
its  contents  should  be  removed  whenever  it  becomes  full. 

A  leaching  cesspool  is  one  not  made  water-tight.  The  liquid 
contents  partly  leach  away  into  the  surrounding  soil,  and  often  into 
sand  or  gravel  strata,  or  crevices  in  the  rock,  which  may  carry  the 
contamination  to  great  distances.  Owing  to  the  offensive  nature  of 
the  work  of  cleaning  out  cesspools,  and  to  the  expense  thereof,  cess- 
pools as  a  usual  thing  are  deliberately  made  not  water-tight.  The 
owner  congratulates  himself  if  he  strikes  a  crevice  in  the  rock  or  a 
gravel  stratum  which  prevents  his  cesspool  from  filling  up,  though 
even  a  little  thought  will  often  show  that  he  is  thus  directly  con- 
taminating the  water  vein  which  supplies  his  own  or  his  neighbor's 
well.  Even  then  he  does  not  usually  escape  permanently  the  expense 
and  annoyance  of  being  forced  to  clean  out  the  cesspool,  for  in  time 
almost  any  crevice  or  porous  stratum  will  clog  so  as  to  permit  only 
partial  escape  of  sewage. 

Leaching  cesspools  should  be  absolutely  prohibited  by  law. 
They  are  even  more  dangerous  than  the  privy,  for  the  liquid  sewage 
in  them  can  penetrate  further  into  the  surrounding  soil  than  the 
faecal  matter  of  the  privy  vault. 

The  frequent  effect  of  cesspools  and  privies  is  illustrated  in 
Fig.  3,  which  does  not  at  all  exaggerate  conditions  very  frequently 
found  in  cities  and  villages.  Often  the  tearing  down  of  old  buildings, 
prior  to  the  erection  of  new,  exposes  to  view  the  rear  of  lots,  and 
shows  sometimes  a  half-dozen  privies  grouped  within  a  few  rods  of 
several  wells.  The  nose  and  the  eye  give  convincing  evidence  of 
foulness  in  such  cases;  and  chemical  or  bacterial  analyses  are  not 
necessary  to  demonstrate  the  danger  in  using  the  wells;  but  the  same 
dangerous  conditions  pass  unnoticed  in  many  other  places  in  the 
same  city,  because  not  exposed  to  casual  view.  In  time,  the  whole 
ground  water  under  such  a  village  or  city  becomes  contaminated,  and 
poisons  wells  and  damp  cellars  and  the  exhalations  from  the  ground. 


SEWERS  AND  DRAINS 


9 


,Cess  Pool 
(Le  aching-  _) 


Well 


6.  A  dry  closet  is  a  privy  having  a  tight,  removable  receptacle 
in  place  of  the  vault,  and  provided  with  means  for  covering  the  con- 
tents with  dry  dust,  ashes,  or  lime  each  time  the  closet  is  used.     Usual- 
ly a  small  shovel  and  a  box  are  used  to  hold  the  dust  or  other  absorbent 
material.     Enough  of  the  dry  material  should  be  used  to  absorb  all 
liquids.     The  contents  should  be  removed  and  hauled  away  in  the 
tight  box  when  it  is  full,  to  be  emptied  in  a  safe  place  or  used  for 
fertilizer.     The  dry  earth  closet  is  an  improvement  over  the  privy 
vault,  but  is  not  a  safe  or  otherwise  satisfactory  arrangement. 

7.  The  pail  system  is  one  in  which  the  faecal  matter  and  urine 
are  received  in  tight  pails,  which  are  removed  daily,  or  at  least  every 
few  days,  by  regular  city  employees.     The  pails  are  carried  to  some 
safe  place,  there 

emptied,  and  re- 
turned  after 
d  i  sin  feet  ion. 
Although  the 
pail  system  has 
been  tried  in 
America  under 
exceptional  con- 
ditions, it  is  en- 
tirely unsuited 
for  use  here,  and 

is  almost  never  employed,  even  in  Europe,  where  the  people  will  sub- 
mit to  the  police  interference  necessary  for  satisfactory  operation. 

8.  Pneumatic  systems  of  sewerage  are  those  in  which  the  sewage 
is  forced  through  the  street  pipes  by  air,  either  by  a  partial  vacuum, 
as  in  the  Liernur  system  (tried  in  Holland),  or  by  compressed  air,  as 
in  the  Berlier  system  (tried  in  France).     Neither  system  is  used  at 
all  in  America,  or  to  any  important  extent  in  Europe.     The  expense 
of  construction  and  operation,  and  the  liability  of  all  such  mechanical 
appliances  frequently  to  get  out  of  order,  make  them  unworthy  of 
consideration. 

9.  Crematory  systems  are  devices  for  disposing  of  faecal  matter, 
urine,  and  garbage  on  the  premises,  by  drying  and  then  burning. 
There  are  several  patented  methods.     The  matter  to  be  disposed  of 
is  received  in  a  furnace-like  structure  on  the  premises,  built  usually 


Fig.  3.    Showing  How  Contamination  of  Well  Water  may  Occur 
through  Proximity  of  Cesspools  and  Other  Sources 
of  Filth. 


10  SEWERS  AND  DRAINS 

of  masonry,  which  is  open  to  a  chimney,  as  well  as  to  the  various 
closets  in  the  building.  The  chimney  is  supposed  to  maintain  a 
current  of  air  out  of  the  rooms  in  which  the  closets  are  located ;  this 
dries  the  material,  which  is  then  burned  at  intervals. 

Where  sewers  have  not  been  available,  crematory  systems  have 
been  installed  in  many  schools  and  other  public  buildings  in  the 
United  States;  but,  while  sometimes  fairly  satisfactory  for  a  while, 
they  are  usually  soon  found  to  be  troublesome,  expensive,  and  danger- 
ous. The  air-currents  sometimes  reverse  into  instead  of  out  of  the 
rooms  containing  the  closets;  danger  ensues  unless  the  burning  is 
regularly  attended  to;  and,  without  constant  care  in  the  attendance, 
the  whole  apparatus  is  likely  to  get  out  of  order.  Moreover,  it  is 
entirely  unadapted  to  the  disposal  of  liquid  wastes  such  as  those 
from  sinks,  washbowls,  laundry  basins,  and  bathtubs,  which  are  ar 
necessary  to  be  taken  care  of  as  fsecal  matter  and  urine. 

In  the  foregoing  paragraphs  (Arts.  4  to  9),  various  makeshifts  fo? 
caring  for  sewage  have  been  described  which  are  not  worthy  the  name 
of  "systems,"  although  the  privy  vault  and  the  cesspool  are  in  verj 
wide  use.  We  next  come  to  the  only  methods  for  removing  sewage 
which  are  at  present  worthy  of  serious  consideration  when  planning  t 
sewerage  system. 

10.  Water-Carriage  Systems.    Water-carriage  systems  of  sewer- 
age are  those  in  which  water  is  added  to  the  fsecal  matter  and  other 
foul  wastes  in  such  quantities  as  to  permit  of  their  rapid  removal  by 
gravity  in  sewers.     As  already  stated,  the  water  so  added  usually 
constitutes  99.8  per  cent  or  more  of  the  resulting  sewage. 

Water-carriage  systems  are  now  so  universally  used  for  sewerage 
purposes,  that  usually  the  two  terms  may  be  considered  synonymous. 
That  is,  in  the  present  day,  a  sewerage  system  is  practically  always 
a  water-carriage  system. 

There  are  two  kinds  of  water-carriage  systems — namely,  the 
Combined  System  and  the  Separate  System. 

11.  Combined  System.    The  combined  system  of  sewerage  is 
that  in  which  the  storm  sewage  flows  in  the  same  sewers  with  the  sani- 
tary and  the  manufacturing  sewage.     The  combined  system  came 
into  use  prior  to  the  separate. 

12.  Separate  System.    The  separate  system  of  sewerage  is  that 


SEWERS  AND  DRAINS  11 

in  which  separate  sewers  are  provided  for  the  storm  sewage  and  for 
/;he  sanitary  and  manufacturing  sewage. 

13.  Comparative  Merits  of  Combined  and  Separate  Systems. 
The  separate  system  came  into  prominence  about  1880.  At  that  time 
and  for  many  years  following,  there  was  an  active  discussion  over  the 
relative  merits  of  the  two  systems,  some  prominent  engineers  advo- 
cating one,  and  some  the  other.  At  the  present  time,  the  discussion 
has  died  down,  and  sanitary  engineers  use  both,  adopting  whichever 
is  best  suited  to  local  conditions,  and  often  using  a  combination  of  the 
two. 

In  favor  of  the  separate  system,  the  following  points  have  been 
cited : 

1.  The  sanitary  sewage  which  constitutes  the  dry-weather  flow 
of  combined  sewers  is  so  very  small  in  comparison  with  the  storm 
sewage,  that  in  circular  sewers,  which  are  the  most  economical  to 
build,  it  forms  merely  a  trickling  stream,  with  little  velocity,  over  the 
bottom  of  the  large  sewers  required ;  while  in  the  separate  system  the 
sewers  are  proportioned  for  this  small  volume,  and  the  sewage  conse- 
quently has  good  depth  and  velocity.     Moreover,  sanitary  sewers  are 
free  from  the  sand  and  other  street  detritus  which  are  inevitably 
washed  into  combined  sewers  during  storms,  and  which  are  especially 
troublesome  in  forming  deposits.     Hence,  in  the  separate  system, 
it  is  easier  to  make  sewers  self -cleansing  from*  deposits. 

2.  Above  the  low-water  line  in  combined  sewers,  the  extensive 
interior  surfaces  of  the  large  sewers  required  become  smeared  with 
filth  in  times  of  flood,  which  remains  to  decay  and  produce  foul  gases 
after  the  flood  subsides. 

3.  On  account  of  the  comparatively  small  size  of  the  sanitary 
sewers  of  the  separate  system,  it  is  easier  to  flush  them  so  as  to  keep 
them  clean.     Automatic  flush-tanks  can  be  used  at  small  expense 
to  do  this  very  satisfactorily. 

4.  On  account  of  the  comparatively  small  size  of  the  sanitary 
sewers  of  the  separate  system,  the  air  in  them  is  much  more  frequently 
and  completely  changed  by  the  daily  fluctuations  in  the  depth   of 
sewage  and  by  the  currents  of  air  through  ordinary  ventilation  open- 
ings.    Hence,  in  the  separate  system,  ventilation  is  easier  and  more 
perfect 


12  SEWERS  AND  DRAINS 

5.  In  case  the  sewage  has  to  be  purified,  the  separate  system  is 
more  economical,  because  only  the  sanitary  sewage  need  be  treated, 
the  storm  sewage  being  discharged  into  nearby  natural  watercourses. 

6.  In  small  cities,  and  in  large  portions  of  large  cities,  the 
storm  water  can  usually  be  carried  some  distance  in  the  gutters,  and 
then  removed  by  comparatively  short  lengths  of  storm  sewers,  laid  at 
shallow  depths  and  discharging  into  the  nearest  suitable  natural 
watercourses.     In  such  cases,  a  separate  system  of  sewers  will  usually 
cost  only  a  fraction,  frequently  only  one-third,  as  much  as  a  combined 
system.     For  small  towns,  the  great  cost  of  a  combined  system  would 
often  prohibit  the  construction  of  sewers  entirely,  or  postpone  it 
almost  indefinitely,  were  it  not  that  a  separate  system  can  be  built  so 
cheaply.     On  this  account  alone,  the  introduction  of  the  separate 
system  of  sewers  has  been  of  incalculable  benefit  in  America. 

7.  On  account  of  their  relatively  small  size,  sewers  of  the 
separate  system  can  be  made  almost  entirely  of  vitrified  sewer-pipe, 
which  has  the  important  advantages  over  brick  sewers,  of  greater 
smoothness,  of  being  impervious,  of  having  few  joints,  and  of  ease  in 
making  the  joints  practically  water-tight.     It  is  impossible  to  make 
even  a  pipe  sewer  absolutely  water-tight,  and  with  brick  sewers  the 
difficulty  is  very  much  greater. 

In  favor  of  the  combined  system,  the  following  allegations,  corre- 
sponding to  the  above  points,  have  been  made : 

1.  By  making  combined  sewers  egg-shaped  with  the  small  end 
down,  or  by  making  a  small,  semicircular  channel  in  the  bottom 
(see  Figs.  19,  24,  and  25),  the  depth  and  velocity  of  the  dry-weather 
flow  can  be  made  sufficient  to  cause  the  sewer  to  be  self-cleansing. 

2.  The  coating  on  the  interior  surface  of  large  sewers  above 
the  low-water  line  is  not  dangerous,  and  in  fact  is  of  very  little  im- 
portance. 

3.  While  it  is  true  that  the  smaller,  separate  sewers  can  be 
flushed  more  perfectly  for  the  same  expense,  the  larger,  combined 
sewers  are  more  convenient  for  removing  obstructions,  and  are  flushed 
out  very  completely  (though  at  too  long  intervals  in  dry  weather)  by 
the  floods  of  storm  sewage  during  rains. 

4.  In  regard  to  ventilation,  the  larger  volume  of  air  over  the 
sewage  in  the  larger,  combined  sewers  dilutes  to  a  much  greater  degree 
the  gases  from  the  sewage. 


SEWERS  AND  DRAINS  13 

5.  In  case  the  sewage  must  be  purified,  it  must  be  remembered 
that  the  early  flow  of  storm  sewage  from  the  streets  is  foul,  to  some 
extent,  from  the  droppings  of  animals  and  other  surface  filth ;  and  it 
may  in  some  cases  be  questionable  whether  this  may  not  require 
purification  in  addition  to  the  sanitary  sewage. 

6.  Wherever,  as  in  the  case  of  the  business  districts  of  large 
cities,  it  is  necessary  to  provide  as  great  a  length  of  storm  sewers  as 
of  sanitary  sewers,  it  will  be  cheaper  to  build  one  set  of  sewers,  as  in  the 
combined  system,  rather  than  two,  as  would  be  required  in  such 
districts  with  the  separate  system. 

The  general  conclusions  of  sanitary  engineers  at  present  regarding 
the  relative  merits  of  the  separate  and  combined  systems,  are  as  follows : 

a.  Either    system  can  be    made  satisfactory  from  a  sanitary 
point  of  view. 

b.  The  cost   of   a  properly  designed    system,  including  means 
for  safe  disposal  of  sewage,  should  ordinarily  decide  which  of  the  two 
systems  should  be  built. 

c.  On  the  basis  of  cost,  the  separate  system  is  usually  the  better 
for  small  cities,  for  suburban  and  sometimes  residence  districts  of 
large  cities,  and  for  all  cases,  even  those  of  large  cities,  where  the 
sanitary  sewage  requires  treatment  while  the  storm  sewage  can  be 
safely  discharged  into  nearby  watercourses.    The  separate  system 
has  just  been  recommended  for  the  city  of  Baltimore  on  this  last 
account. 

d.  Similarly,  on  the  basis  of  cost,  the  combined  system  is  usually 
the  best  for  the  business  and  other  very  thickly  built-up  districts  of 
large  cities,  and,  in  general,  where  storm  sewers  must  be  coextensive 
with  sanitary  sewers;  also  for  cases  where  both   storm  sewage  and 
sanitary  sewage  require  purification. 

e.  Often  a  combination   of  the  two  systems  can  be  made   to 
advantage,  storm  water  being  admitted  to  the  sewers  only  in  certain 
portions  of  the  system,  such  as  the  business  districts. 

GENERAL  FEATURES  OF  SEWERS 

14.  Kinds  of  Sewers.  Sanitary  sewers  are  those  constructed  to 
carry,  foul  waste  liquids  of  human  or  animal  origin — that  is,  sanitary 
sewage.  Since  sewage  of  human  or  animal  origin  is  most  apt  to 
contain  the  germs  of  human  diseases,  sanitary  sewers  require  special 


14 


SEWERS  AND  DRAINS 


Court   House 
Square 


precautions  in  design,  construction,  and  maintenance,  to  render  them 
safe.  Manufacturing  sewage  is  often,  however,  even  stronger  and 
more  offensive  than  sanitary  sewage,  and  hence  requires  equal  pre- 
cautions. In  the  separate  system,  the  manufacturing  sewage  should 
go  into  the  sanitary  sewers  or  into  special  sewers  of  similar  character. 

Combined  sewers  are 
those  constructed  to  carry 
both  sanitary  sewage  and 
storm  sewage.  With  the 
combined  system,  the 
manufacturing  sewage 
also  usually  goes  into 
the  combined  sewers. 

Storm  sewers  are  those 
constructed  to  carry 
storm  sewage  only. 

An  outlet  sewer  is  one 
connecting  a  sewer  sys- 
tem, or  a  part  thereof, 
with  the  point  of  final 
discharge  of  the  sewage. 
A  main  sewer,  or  sewer 
main,  is  the  principal 
sewer  of  a  city,  or  of  a 
large  district  thereof,  into 
which  branch  sewers 
discharge. 

A  sub^main  sewer  is  a 
branch  of  a  main  sewer, 
receiving  in  its  turn  the 
discharge  of  smaller 
branches. 

A  lateral  sewer  is  one  not  receiving  the  discharge  of  other  sewers, 
hence  serving  only  property  closely  adjacent. 

In  Fig.  4,  the  various  kinds  of  sewers  above  described  are  shown, 
from  a  portion  of  the  actual  sewerage  map  of  a  small  city,  sewered  on 
the  separate  system. 

15.    Intercepting  sewers  are  those  built  across  lines  of  other 


Manholes 
Lampbolea 
Flush  Tanks 
Street  Inlets 


Cre-etv 


Fig.  4.  Kinds^of  Sewers  and  Arrangement  of 
Accessories. 


SEWERS  AND  DRAINS 


15 


La: 


Intercepting-  Sewers 

Lake  View  Crib 


Carter  H.Harrison  CviT* 
•2  Mile   Crib 


A  Mile  Crib 


sewers,  to  intercept  the  sewage  flowing  in  them  and  carry  it  away  to 
different  outlets. 

In  Fig.  5  are  shown  the  intercepting  sewers  of  the  city  of  Chicago, 
built  along  the  lake  front  to  intercept  the  sewage  in  the  sewers  which 
formerly  discharged  into  and  polluted  Lake  Michigan,  from  which 
the  water  supply  of  the  city  is  taken.  From  the  intercepting  sewers, 
the  sewage  is  pumped  into  the  Chicago  River,  which  now  discharges 
through  the  great 
Drainage  Canal 
into  the  Des- 
plaines  river,  the 
Illinois  River, 
the  Mississippi 
River,  and  the 
Gulf  of  Mexico, 

16.  General 
Description  o  f 
Sewers.  Sewers, 
as  usually  built, 
are  smooth  pipe 
or  masonry  con- 
duits, as  nearly 
water-tight  a  s 
practicable,  bur- 
ied in  the  ground 
as  deeply  as  nec- 
essary to  serve 
the  adjacent 

houses  and  drain  other  territory  tributary  upstream.  They  are  very 
carefully  constructed  to  an  exact  grade  line,  determined  by  the  engi- 
neer who  made  the  sewer  plans. 

Unless  special  circumstances  require  other  forms,  sewers  are 
usually  made  circular,  this  shape  giving  the  greatest  strength  and 
area  for  a  given  amount  of  material.  For  other  shapes,  and  the 
circumstances  to  which  they  are  adapted,  see  Figs.  19  to  25. 

The  invert  of  a  sewer  is  the  lowest  point  on  the  interior  surface 
(being  so  called  because  the  interior  curve  is  there  inverted).  When 
the  grade  of  a  sewer  is  mentioned,  or  the  elevation  of  the  sewer  at  a 


Intercepting  Sewers 


.mpincf  Station 
ntercepting-  Sewer  s 


Q 

th  St-Crilo 


Fig.  5.    Intercepting  Sewers  of  the  City  of  Chicago,  111. 


16 


SEWERS  AND  DRAINS 


given  place  is  spoken  of,  the  invert  is  always  meant.  The  invert  is 
also  sometimes  called  the  flow  line. 

Almost  all  sewers  up  to  24  inches'  diameter,  and  many  from  24 
to  36  inches'  diameter,  are  made  of  vitrified  or  cement  pipe.  Above 
these  sizes,  concrete  or  brick  masonry  is  ordinarily  used.  Stone 
masonry  and  iron  pipe  are  also  used,  but  only  seldom.  A  comparison 
of  these  materials  is  given  elsewhere  in  this  paper. 

At  intervals  along  sewers,  manholes  (Art.  21)  and  lampholes 
(Art.  22)  are  placed  to  permit  examination  and  repairs,  and  often 
flush-tanks  (Art.  23)  are  provided  to  keep  the  sewers  clean.  In  the 
case  of  storm  sewers  and  combined  sewers,  either  street  inlets  or  catch- 


Dwelling 


& 

Fig.  6.    Street  Sewer,  Subdrain,  and  House  Connection. 

basins  (Art.  27)  must  be  provided,  for  admitting  the  storm  water  to 
the  sewers.  These  are  usually  placed  at  or  near  the  curb  corners  at 
the  street  intersections. 

A  general  idea  of  the  relation  of  a  sewer  to  a  building  served  by 
it,  may  be  gained  from  Fig.  6.  The  sewer  there  shown  is  a  pipe 
sewer.  Usually  all  lateral  sewers  are  made  of  pipe;  and  in  the 
separate  system,  the  submains  and  mains  also,  unless  the  city  is  quite 
large. 

17.  Location  of  Sewers.  Sanitary  sewers  are  usually  placed 
on  the  center  lines  of  the  streets,  so  as  to  give  equal  fall  from  the  houses 
on  both  sides.  On  this  account,  water,  gas,  and  heating  mains, 
storm  sewers,  and  other  conduits  should  be  constructed  far  enough 
from  the  center  lines  not  to  interfere  with  the  sanitary  sewers.  Not 


SEWERS  AND  DRAINS  17 

infrequently  the  center  of  the  street  is  found  already  occupied  by  other 
conduits  which  were  located  without  proper  foresight;  and  it  is  then 
necessary  to  place  the  sewer  nearer  to  one  side  than  the  other. 

In  cases  of  streets  on  side  hills,  it  is  sometimes  necessary  to  place 
the  sewer  close  to  the  downhill  side  of  the  street,  in  order  to  serve 
houses  on  that  side  which  are  lower  than  the  street  grades. 

In  a  few  cases  of  excessively  wide  avenues,  especially  if  paved,  it 
is  cheaper  to  build  two  lines  of  sanitary  sewers,  one  on  each  side,  than 
to  construct  the  longer  house  connections  required. 

In  any  town  having  a  fairly  extensive  system  of  alleys,  careful 
consideration  should  be  given  by  the  sewerage  engineer  to  the  feasi- 
bility and  desirability  of  locating  part  or  all  of  the  sanitary  sewers  in 
them  instead  of  in  the  street.  In  Memphis,  this  plan  was  followed  as 
far  as  practicable.  It  is  not  usually  feasible  to  locate  combined  or 
storm  sewers  in  alleys,  because  such  sewers  must  receive  storm  water 
from  the  streets  running  in  both  directions,  and  hence  must  usually 
have  the  street  inlets  placed  at  the  street  corners. 

Streets  vs.  Alleys  for  Sanitary  Sewers.  Location  of  the  sanitary 
sewers  in  the  alleys  has  a  great  advantage  in  avoiding  the  tearing  up 
of  the  streets  and  pavements  for  sewer  repairs  and  for  new  house 
connections,  which  not  infrequently  causes  them  serious  injury. 
Pavements  are  often  ruined  by  the  trenches  dug  for  water,  sewer,  gas, 
and  other  connections.  Also,  if  the  sewers  are  in  the  alleys,  the 
trenches  for  house  connections  do  not  cross  the  lawns  in  front  of  the 
houses. 

On  the  other  hand,  the  system  of  alleys  in  the  ordinary  town  is 
a  public  nuisance.  They  are  usually  filled  mainly  with  manure  piles, 
garbage,  and  debris  of  all  descriptions;  and  they  open  through  the 
middle  of  the  blocks  vistas  which  suggest  most  forcibly  a  neglected 
city  dumping  ground.  Owing  to  their  vile  sanitary  condition,  the 
alleys  are  usually  the  first  danger  spots  demanding  attention  when 
a  town  is  threatened  with  an  epidemic.  Except  in  the  business 
districts  where  they  can  be  paved  and  policed,  there  is  no  necessity 
for  alleys  unless  the  lots  are  very  narrow,  for  in  almost  every  town 
there  are  sections  which  do  without  and  never  miss  them.  Teams 
can  without  inconvenience  drive  in  from  the  front,  along  a  cinder  or 
gravel  drive.  Such  sections  are  better  off  without  the  alleys,  from 
both  the  sanitary  and  the  aesthetic  points  of  view. 


18  SEWERS  AND  DRAINS 

For  the  above  reasons,  it  is  often  unwise  to  perpetuate,  or  perhaps 
even  extend,  the  alley  system  by  locating  sewers  in  them. 

Again,  the  system  of  alleys,  more  often  than  not,  is  far  from  being 
as  complete  as  the  street  system ;  and  in  such  cases  it  will  usually  add 
considerably  to  the  total  length  of  sewers  required  to  serve  a  given 
territory,  if  part  of  them  are  placed  in  the  alleySo  The  alleys,  also, 
are  usually  too  narrow  to  permit  the  construction  of  sewers  of  con- 
siderable depth,  without  trouble  as  regards  the  excavated  material, 
the  handling  of  pipe,  etc.  Moreover,  houses  and  the  fixtures  in 
them  are  usually  so  located  that  the  house  connection  would  be 
longer  to  the  alley  than  to  the  street,  requiring  a  deeper  sewer  for 
equal  service.  This,  however,  is  not  always  the  case. 

The  sanitary  engineer  should  study  each  town  by  itself,  and 
decide  this  question  after  giving  due  weight  to  all  these  various  con- 
siderations. 

18.  Depth  of  Sewers:  The  depth  of  sanitary  and  combined 
sewers  should  be  great  enough  to  afford  good  drainage  to  the  base- 
ments of  all  buildings.  This  will  usually  call  for  the  tops  of  the  sewers 
to  be  about  3J  feet  below  the  basement  floors,  as  follows: 

MINIMUM  DEPTHS  FOR  SANITARY  AND  COMBINED  SEWERS 

Fall  from  sewer  to  house 2  ft.  0  in. 

Fall  from  basement  floor  to  house  connection 1  ft.  6  in. 

Total  from  top  of  sewer  to  basement  floor 3  ft.  6  in. 

For  sewer  laterals,  add  to  the  above  for  fall  at  sewer 1  ft.  0  in. 

Total  from  invert  of  lateral  sewer  to  basement  floor 4  ft.  6  in. 

For  residence  districts,  add  for   ordinary-depth   basements  below 

street  level 4  ft.  0  in. 

Total  minimum  depth  to  invert,  of  lateral  sewers  in  residence 

districts 8  ft.  6  in. 

For  business  districts,  add  for  ordinary-depth  basements  ......   8  ft.  0  in. 

Total  minimum  depth  to  invert  of  lateral  sewers  in  business 

districts 1 2  ft.  0  in. 

Hence,  under  average  conditions,  the  depth  of  sanitary  and  combined 
pipe  sewers  of  12-inch  diameter  and  less,  should  be  not  less  than  8} 
feet  in  residence  districts,  and  12J  feet  in  business  districts.  If, 
however,  there  is  only  a  short  stretch  of  low-lying  ground  on  a  residence 
street,  it  may  be  advisable  to  reduce  the  above  depth,  say  to  6  feet  as 
a  minimun,  when  by  so  doing  a  very  long  stretch  of  sewer  can  be 
lessened  that  much  in  depth  throughout,  and  a  large  saving  in  cost 
made  thereby. 


SEWERS  AND  DRAINS  19 

In  the  case  of  sanitary  and  combined  sewers  more  than  12  inches 
in  height,  the  above  depths  should  be  increased  by  the  excess  over  12 
inches,  for  the  house  connections  should  enter  near  the  top  of  the 
sewer. 

In  the  case  of  storm  sewers  and  of  outlet  and  intercepting  sewers, 
the  depth  will  no  longer  be  determined  by  the  depth  of  basements 
alongside.  In  these  sewers  three  other  considerations  determine  the 
depth:  (1)  the  depth  at  the  upper  end  necessary  to  afford  a  good 
outlet  for  the  sewage;  (2)  the  grade  necessary  to  give  good  velocity; 
(3)  the  depth  necessary  to  prevent  injurious  heaving  of  the  sewer 
foundations  by  frost. 

In  regard  to  the  third  point,  no  danger  need  be  apprehended  of 
the  sewer  itself  freezing  up,  even  if  it  be  laid  practically  at  the  surface, 
for  a  stream  of  warm,  flowing  sewage  will  not  freeze.  There  will  be 
little  or  no  danger  of  trouble  from  heaving,  if  the  sewer  foundation  be 
four  feet  under  ground ;  and  many  stretches  of  pipe  sewers  only  two 
or  three  feet  deep  operate  with  entire  satisfaction  even  in  the  northern 
United  States. 

19.  Subdrains.  It  has  already  been  stated  that  sewers  should 
be  made  as  nearly  water-tight  as  possible.  Otherwise  there  would 
be  danger  of  the  sewage  leaking  out  so  as  to  contaminate  the  adjacent 
soil.  Hence,  while  it  is  not  possible  at  any  reasonable  expense  to 
make  sewers  absolutely  tight,  they  should  be  built  with  the  utmost 
care  in  this  particular. 

Yet,  when  due  care  is  used  in  this  respect,  the  sewer  is  made 
unfit  for  performing  another  important  duty — that  of  draining  away 
subsoil  water  so  as  to  dry  out  unwholesome  dampness  from  the  soil, 
and  especially  from  wet  cellars  and  from  under  and  around  houses 
built  on  low  ground. 

In  order  to  secure  such  drainage,  and  also,  in  case  of  wet  ditches, 
to  help  remove  water  from  the  trenches  during  construction,  it  often 
becomes  necessary  or  advisable  to  add  to  the  sewer  a  subdrain. 

A  subdrain  is  a  line  of  drain  tile  or  sewer  pipe  laid  with  open 
joints,  in  the  same  trench  with  the  sewer. 

To  allow  connections  with  cellar  drains  to  be  made  from  both 
sides  of  the  streets,  the  subdrain  should  be  placed  with  its  top  a  few 
inches  below  the  bottom  of  the  sewer;  and  to  leave  a  firm  foundation 


20  SEWERS  AND  DRAINS 

for  the  sewer  itself,  the  subdrain  should  be  placed  a  little  to  one  side 
D£  the  sewer. 

With  the  above  arrangement,  special  care  should  be  taken  to 
make  the  sewer  joints  tight,  and  there  is  some  danger  of  slight  leakage 
of  sewage  into  the  subdrain.  Such  leaks  tend  to  stop  themselves 
as  time  passes. 

It  is  not  safe  to  connect  cellar  drains  directly  with  a  sewer,  even 
though  they  are  trapped  to  prevent  the  sewer  air  from  penetrating 
into  and  filling  the  pores  of  the  soil  under  houses.  In  dry  times, 
there  may  be  no  water  running  in  the  cellar  drains;  and  at  such  times 
the  water  in  a  trap  may  evaporate  so  as  to  unseal  it.  Cellar  and 
foundation  drains  should  be  connected  to  the  subdrain  instead  of  to 
the  sewer  itself. 

The  general  relation  of  the  subdrain  to  the  sewer  in  the  street, 
and  the  method  of  connecting  it  with  the  foundation  drains,  may 
be  seen  in  Fig.  6. 

In  construction,  the  joints  of  the  subdrain  should  usually 
be  wrapped  with  muslin  to  prevent  the  entrance  of  mud  and  sand. 
The  cloth,  of  course,  does  not  last  long;  but  by  the  time  it  rots,  the 
soil  around  the  tile  will  usually  have  become  recompacted  so  that  there 
is  no  longer  danger  of  its  getting  into  the  drain.  In  quicksand,  it 
may  sometimes  be  necessary  to  fill  in  fine  pebbles  or  broken  stone 
around  the  subdrain. 

20.  House  Connections.  In  Fig.  6  is  also  shown  the  method  of 
connecting  the  sewer  itself  with  the  iron  soil-pipe  which  drains  the 
different  plumbing  fixtures,  and  which  should  ex- 
tend at  least  6  feet  outside  the  basement  wall.  The 
house  connection  should  be  a  line  of  4-inch  vitrified 
sewer-pipe,  laid  at  right  angles  to  the  sewer,  with 
tightly  cemented  joints,  and  if  possible  to  at  least  a 
2  per  cent  grade  (that  is,  with  a  fall  of  2  feet  in  100 
Fig.  ?.  junction  feet  length).  Some  prefer  6-inch  house  connections; 

of  House  Connec- 


tisewerth  kut  tnese  should  not  be  allowed  with  8-inch  sewers, 
as  the  house  connection  may  then  allow  obstructions 
to  be  carried  to  the  street  sewer  large  enough  to  catch  therein  and 
cause  stoppages.  At  the  sewer,  the  house  connection  should  turndown, 
by  a  4-inch  45-degree  elbow,  into  a  4-inch  Y-junction  laid  so  as  to 
slant  upward  45  degrees  —  all  as  shown  in  Fig.  7.  This  slant  upward 


SEWERS  AND  DRAINS 


21 


^-  Contractor 
Stop  Hera 


_  4-"  Sewer  Pipe 
Bella  Up 


_«4\Sewer  Pipe 
Bells  Down 

.  .rtland 
Cement  Concrete 


keeps  the  Y  from  affecting  the  smooth  ordinary  flow  in  the  sewer. 

In  case  the  sewer  is  more  than  12  feet  deep  below  the  street 
surface,  the  expense  of  digging  down  to  it  in  making  house  connec- 
tions would  be  so  great  that  it  is  usually  better,  while  the  trench  is 
open  during  sewer  construction,  to  put  in  a 
deep-cut  house  connection,  as  shown  in  Fig.  8. 
In  this  case,  sewer  pipe  must  be  used  from  the 
subdrain  also,  if  such  a  drain  is  used;  and  care 
should  be  taken  to  turn  the  bells  of  the  subdrain 
connection  down  so  that  the  plumbers  need 
make  no  mistake  in  the  connections  afterwards. 

In  sewer  construction,  a  Y-junction  for  a 
house  connection  (or  a  deep-cut  house  connec- 

.«    ,1  •  1  r>  f          j         \      i        11      Fig.  8.      Deep-Cut  House 

tion,  if  the  sewer  is  over  12  leet  deep),  should  connection. 

be  conveniently  located    opposite  each  lot  on 

each  side  of  the  sewer;  and  the  ends  should  be  stopped  with  vitrified 
stoppers,  covered  over  with  sand  and  then  cemented  in.  Full  and 
accurate  records  must  be  kept  of  the  exact  locations  of  these  con- 
nections, so  that  they  can  be  found  without  trouble  at  any  time. 

No  person  should  be  allowed  to  cut  or  break  into  a  pipe  sewer 
for  making  house  connections  or  any  other  kind  of  junction.  If  there 
is  no  Y  or  T-branch  already  set  for  the  connection,  a  full  length  of 
pipe  should  be  broken  out  and  the  proper  Y  or  T-branch  inserted 
A  skilful  workman  can  readily  do  this  by  breaking  off  one-half  the 
bell  of  the  new  pipe,  and  of  that  of  the  old  piece  into  which  it  must 
be  inserted,  and  turning  the  new  piece  half  around  after  insertion. 
The  joints  must  then  be  re-cemented  with  great  care. 

21.  Manholes.  It  has  already  been  stated  (Art.  16)  that  man- 
holes must  be  placed  at  intervals  along  sewers,  to  permit  of  examina- 
tion and  repairs.  These  manholes  are  usually  circular  brick  wells, 
with  Portland  cement  concrete  bottoms  and  heavy  cast-iron  covers, 
as  shown  in  detail  in  Fig.  9.  They  must  be  large  enough  at  the  bottom, 
and  for  a  couple  of  feet  above  the  top  of  a  pipe  sewer,  to  permit  a 
man  to  work  comfortably.  Four  feet  in  diameter  is  a  satisfactory 
size.  Sometimes  the  manholes  are  made  elliptical  at  the  bottom, 
with  the  long  axis  lengthwise  of  the  sewer;  but  this  form  is  more 
difficult  to  build.  Above  the  point  mentioned,  the  sewer  may  be 
drawn  in  gradually  to  a  diameter  of  about  2  feet  9  inches,  at  a  point 


22  SEWERS  AND  DRAINS 

2  feet  9  inches  below  the  street  surface,  and  thence  narrowed  more 
rapidly  to  about  20  inches  diameter  at  the  bottom  of  the  cover  casting. 
The  cover  casting  may  be  of  any  manufacturer's  design  satis- 
factory to  the  engineer,  weighing  at  least  375  Ibs.  The  lid  should 
usually  be  perforated  with  1-inch  holes,  to  permit  ventilation  of  the 
sewer;  and  immediately  below  it,  there  should  be  hung  a  heavy  cast- 
iron  dustpan,  to  catch  any  dirt  entering  through  the  perforations. 

There  should  be  a  ladder  of  iron  rungs  built  into  the  walls,  as 
shown  in  Fig.  9. 

The  channels  in  the  concrete  bottom  should  be  very  carefully 
formed  to  give  smooth,  true,  circular  channels.  They  are  some- 
times lined  with  split  sewer  pipe.  The  benches  at  the  sides  of  tfap 
channels  should  slope  down  towards  the  channels,  as  shown  in  the 
figure. 

The  concrete  for  the  bottom  may  be  made  of  1  part  Portlan  I 
cement,  3  parts  sand,  and  5  parts  of  broken  stone.  All  the  brick  - 

work  should  be  laid  with  tight  show 
joints,  in  l-to-3  Portland  cement  mor- 
tar;  and  the  manhole  walls  should  be 
plastered  both  inside  and  outside  with 
l-to-2  Portland  cement  mortar. 

Should  sudden  drops  in  the  sewer  be 
desirable,  they  can  be  made  at  drop 
manholes,  in  the  manner  shown  by  the 
broken  lines  of  Fig.  9. 

In  the  case  of  large  masonry  sewers, 
which  often  are  many  feet  in  diameter 
the  manholes  may  be  joined  directly 

Fig.  9.    Sectional  Elevation  and  Plan    to   the  masonry   of  the   Upper   part    of 
of  Sewer  Manhole, 

the  sewer. 

Opinions  of  sanitary  engineers  differ  somewhat  as  tc  the  distance 
apart  at  which  manholes  should  be  placed.  In  general,  a  manhole 
should  be  placed  at  all  junctions  of  sewers,  and  at  every  change  uf 
grade  or  alignment  in  all  sewers  but  those  large  enough  to  tje  entered 
readily  for  cleaning.  This  means  that  sewers  should  ordinarily  be 
perfectly  straight  between  manholes,  to  facilitate  inspection  and 
repairs,  all  changes  in  both  grade  and  alignment  being  made  at  the 
manholes  themselves 


SEWERS  AND  DRAINS  23 

Also,  in  any  part  of  the  system — such  as  in  the  business  district — 
where  it  is  especially  objectionable  to  have  the  street  dug  up  for  repairs, 
manholes  should  be  placed  at  least  as  often  as  every  city  block — that 
is,  300  to  400  feet  apart.  In  the  other  parts  of  the  system,  some 
engineers  leave  out  every  other  manhole  where  the  grade  and  align- 
ment are  straight,  putting  manholes  at  least  every  two  blocks.  The 
intermediate  manholes  left  out  are  replaced  by  lampholes  (Art.  22) 
to  save  cost.  In  Figs.  4  and  38,  the  above  arrangement  of  manholes 
is  shown  in  two  actual  sewer  systems. 

22.  Lampholes.    The  lampholes  which,  to  save  cost,  are  some- 
times adopted  in  place  of  part  of  the  manholes,  consist  each  of  a 
vertical  line  of  sewer  pipe,  with  cemented  joints,  reaching  to  the  street 
surface,  as  in  Fig.  10.     Usually  8  inches  is  the  min- 

imum  diameter  for  this  pipe,  which  is  cemented  at 
the  bottom  into  a  regular  sewer-pipe  T-junction. 
Some  concrete  should  be  placed  under  and  around 
this  tee  for  a  foundation.  At  the  street  surface,  there 
should  be  an  iron  casting  similar  to  a  manhole  cast- 
ing, but  smaller,  as  shown  in  Fig.  10. 

The  earth,  in  refilling,  needs  to  be  very  thor- 
oughly tamped  around  the  lamphole ;  and  the  lamphole  casting  should 
not  be  set  until  the  material  is  thoroughly  settled. 

The  object  of  the  lamphole  is  to  permit  of  inspection  of  the  sewer, 
in  determining  whether  it  is  clean  and  in  locating  stoppages.  While 
its  name  suggests  the  lowering  into  it  of  a  lamp,  a  beam  of  sunlight 
reflected  into  it  from  a  mirror  is  more  convenient. 

A  lamphole  usually  costs  about  $30  to  $35  less  than  a  manhole. 

In  Figs.  4  and  38  the  above  arrangement  of  lampholes  in  two 
actual  sewer  systems  may  be  seen. 

23.  Flush-Tanks.     Near  the  upper  ends  of  sewers  the  flow  of 
sewage  is  very  small,  sufficient  only  to  make   a   shallow,  trickling 
stream,  liable  not  to  be  able  to  carry  along  the  solid  matter  in  the 
sewage  so  as  to  prevent  deposits.     An  8-inch  lateral  sewer  in  a  resi- 
dence district  in  a  small  town,  even  if  laid  at  the  minimum  grade, 
would  usually  have  an  average  depth  of  flow  in  the  upper  two  and  one- 
half  blocks  of  less  than  one  inch.     Hence  it  is  desirable,  though  not 
always  absolutely  necessary,   to  provide  some  special  means  for 


24 


SEWERS  AND  DRAINS 


regularly  flushing  th?  upper  portions  of  sewer  laterals,  to  make  them 
self-cleansing. 

Again,  in  low-lying,  level  districts,  it  may  be  necessary,  on  account 
of  the  lack  of  fall,  to  lay  the  sewers  at  such  slight  grades  that  the 
velocity  is  insufficient  to  prevent  deposits.  Here,  too,  some  special 
means  should  be  provided  for  regularly  flushing  the  sewers. 

In  the  case  of  pipe  sewers,  such  as  are  ordinarily  used  for  the 
laterals  in  all  systems,  and  for  most  of  the  mains  in  separate  systems. 


S<pHor»  Main  Trap 
Auxiliary  Trap 


Fig.  11.    Sewer  Flush-Tank  with  "  De  La  Hunt "  Adjustable  Siphon. 

the  most  efficient  and  reliable  means  for  securing  regular  flushing  is 
the  use  of  automatic  flush-tanks. 

A  flush-tank  is  a  masonry  cistern  built  in  the  street,  above  the 
grade  of  the  sewer,  filled  by  a  constantly  running  stream  of  water 
brought  by  a  small  pipe  from  the  water-supply  mains,  and  suddenly 
emptied  by  automatic  devices  into  the  sewer  whenever  the  high-water 
line  is  reached. 

Flush-tanks  usually  have  a  capacity  of  150  to  500  gallons,  and 
should  approach  the  larger  size  named,  to  secure  an  efficient  flush 


SEWERS  AND  DRAINS 


25 


for  two  or  three  blocks.  When  made  separate  from  manholes,  flush- 
tanks  are  usually  circular  and  of  the  general  design  of  the  masonry 
tank  shown  in  Fig.  11.  It  is  usually  better,  however,  to  combine  the 
flush-tank  with  a  manhole,  as  is  shown  by  the  masonry  tank  and  man- 
hole in  Fig.  12.  This  permits  inspection  of  the  flush-tank  and  sewer, 
and  is  cheaper  than  to  build  manhole  and  flush-tank  separate. 

The  bottoms  of  flush-tanks  are  usually  of  Portland  cement  con- 
crete, and  the  walls  of  brick  laid  in  Portland  cement  mortar.      The 


Fig.  12.    Combined  Flush-Tank  and  Manhole  with  Special  • '  Miller  "  Siphon. 

tanks  should  be  plastered  inside  and  outside  as  described  for  manholes 
(see  Art.  21).  Special  care  should  be  used  to  make  flush-tanks  abso- 
lutely water-tight. 

The  water  is  usually  brought  to  the  flush-tank  by  a  f-inch  gal- 
vanized pipe  from  the  nearest  water  main.  This  pipe  must  be  laid 
below  the  frost  line  (5J  to  7  feet  deep,  in  the  northern  part  of  the 
United  States),  but  should  be  turned  up  after  it  enters  the  flush-tank 
so  as  to  discharge  above  the  high-water  line,  as  shown  in  Fig.  11. 


26  SEWERS  AND  DRAINS 

The  flush-tank  may  be  prevented  from  freezing  by  being  con- 
nected with  the  sewer  above  the  high- water  line,  as  shown  in  Figs.  1 1 
and  12,  so  as  to  admit  the  warm  air  from  the  sewer. 

It  is  a  quite  common  practice  to  place  flush-tanks  at  the  heads 
of  all  laterals,  as  illustrated  in  Figs.  4  and  38.  While  some  engineers 
dispute  the  necessity  for  this,  it  must  be  admitted  that  such  an  arrange- 
ment will  be  of  great  benefit,  and  its  adoption  is  here  advised  for  most 
cases. 

In  Fig.  38  the  use  of  flush-tanks  is  shown  at  certain  half-way 
points  on  the  long  laterals.  The  necessity  for  this  arose  from  the 
fact  that  the  sewers  were  not  to  be  completed  to  the  north  ends  of  the 
laterals  for  some  years  after  the  southern  portions  were  built. 

The  writer  of  this  paper  has  used  flush-tanks  with  success  and 
great  benefit,  at  intervals  of  about  two  or  three  blocks  on  sewers  laid 
at  grades  below  those  considered  necessary  to  make  the  sewers  self- 
cleansing,  though  part  of  the  flush  from  the  intermediate  tanks  flows 
some  distance  upstream  at  each  discharge. 

The  flush-tanks  of  a  sewer  system  should  be  frequently  in- 
spected after  the  sewers  are  put  into  operation,  and  should  be  care- 
fully kept  in  working  order.  The  things  needing  most  faithful  watch- 
ing are:  first,  the  automatic  discharging  apparatus;  and,  second,  the 
supply  of  water.  The  faucet  admitting  water  may  readily  become 
choked  up,  putting  the  flush-tank  out  of  service,  or,  on  the  other  hand, 
may  get  wide  open,  wasting  thousands  of  gallons  of  water  every  day. 

24.  Automatic  Flushing  Siphons.  The  reliability  of  flush-tanks 
in  actual  use  will  depend  upon  the  frequency  and  care  with  which  they 
are  inspected  and  kept  in  working  order,  and  especially  on  the  relia- 
bility of  the  automatic  discharging  apparatus.  No  discharging 
apparatus  having  moving  parts  should  be  used  in  flush-tanks.  Such 
apparatus  is  too  likely  to  get  out  of  order. 

In  Figs.  11  and  12,  sewer  siphons  are  shown  for  automatically 
discharging  the  flush-tanks  suddenly  whenever  they  fill  to  the  high- 
water  line.  Such  siphons  have  no  moving  parts  whatever  to  get  out 
of  order,  and  should  always  be  employed  with  flush-tanks. 

In  Fig.  11  the  four  ordinary  parts  of  a  flushing  siphon  are  indi- 
cated. All  four  are  usually  iron  castings,  and  must  be  air-tight. 
The  siphvn  bell  rests  upon  the  main  trap,  which  latter,  together  with 
the  auxiliary  trap,  must  be  filled  with  water  to  the  heights  of  the 


SEWERS  AND  DRAINS  27 

short  legs,  before  the  bell  is  placed  in  position.  The  main  trap  must 
be  set  plumb.  The  auxiliary  siphon  serves  to  ensure,  at  the  end  of 
the  discharge,  the  venting  of  the  siphon — that  is,  the  free  admission 
of  air  to  the  inside  of  the  bell.  With  clear  water,  the  auxiliary 
siphon  is  not  always  used ;  but  it  should  be  used  whenever  the  siphon 
is  to  be  used  with  raw  sewage. 

In  the  working  of  the  siphon,  the  water  in  the  flush-tank  con- 
fines the  air  inside  the  bell  and  above  the  water  in  the  main  and  auxili- 
ary traps,  and  puts  it  under  increasing  pressure  as  the  water  rises. 
When  the  high-water  line  in  the  flush-tank  is  reached,  this  pressure 
becomes  so  great  that  the  water  in  the  auxiliary  trap  is  forced  down 
to  the  very  bottom  of  the  trap,  and  the  confined  air  then  blows  out 
of  the  short  leg  of  the  auxiliary  trap,  thus  releasing  the  air-pressure 
inside  the  bell,  which  up  to  this  time  has  held  back  the  water  in  the 
flush-tankc  The  water  in  the  flush-tank  then  rushes  out  into  the 
sewer  through  the  main  trap,  and  by  siphonic  action  will  continue  to 
flow  out  until  drawn  down  to  the  level  of  the  bottom  of  the  bell.  Air 
then  enters  the  bell  through  a  small  sniff-hole  provided  near  the  bottom 
of  the  bell  for  this  purpose,  breaking  the  siphonic  action — that  is, 
venting  the  siphon. 

In  case  a  siphon  is  used  for  raw  sewage,  there  is  often  difficulty 
n  securing  satisfactory  venting  of  the  siphon  at  the  close  of  the  dis- 
charge; but  this  trouble  can  be  remedied  by  using  an  auxiliary  siphon, 
as  shown  in  Fig.  11,  and  as  illustrated  by  broken  lines  for  the  "Miller" 
siphon  in  Fig.  12. 

In  the  Miller  siphon,  shown  in  Fig.  12,  there  is  no  auxiliary  trap; 
but  at  high-water  line  the  air-pressure  in  the  main  trap  becomes  so 
great  that  a  bubble  escapes,  taking  with  it  enough  water  from  the 
short  leg  to  start  a  sudden  rush  of  water  from  the  tank  into  the  main 
trap,  which  suffices  to  establish  siphonic  action.  This  greatly  simpli- 
fies the  siphon;  and  the  principle  can  be  relied  upon  for  siphons  not 
larger  than  about  eight  inches  internal  diameter  of  the  main  trap. 
Larger  siphons  should  have  auxiliary  traps. 

In  some  siphons — as,  for  example,  the  Rhoads-Miller — the 
auxiliary  trap  is  cast  as  a  part  of  the  main  trap,  out  of  which  it 
opens  below  the  floor  of  the  tank,  being  entirely  buried  out  of  sight 
and  reach  in  concrete.  An  objection  to  auxiliary  traps  such  as  shown 
in  Fig.  11,  is  that  they  are  inaccessible  and  may  in  time1  become 


28  SEWERS  AND  DRAINS 

stopped  up.     However,  they  make  the  action  of  large  siphons  more 
certain. 

25.  Hand-Flushing  of  Sewers.     For  large  sewers,  flush-tanks 
and  siphons  would  have  to  be  extremely  large  to  be  effective.     Even 
in  small  sewers  the  effect  of  the  flush  will  not  be  great  for  many  blocks 
below  the  tank.     Some  engineers  doubt  the  necessity  for  very  exten- 
sive use  of  flush-tanks.     When  flush-tanks  are  not  properly  inspected 
and  regulated  (as  to  the  feed  faucet),  they  sometimes  waste  great 
quantities  of  city  water.     For  these  reasons,  and  sometimes  to  save 
cost,  hand  methods  are  sometimes  relied  upon  for  flushing  sewers. 

The  most  convenient,  economical,  and  effective  hand-flushing 
device  is  a  connection  with  a  water  main  by  a  water  pipe  of  size  large 
enough  to  flush  the  sewer  very  thoroughly.  The  only  labor  then 
required  is  that  necessary  for  opening  and  closing  the  valves  on  this 
pipe.  Such  a  flush,  continuing  much  longer  than  the  discharge  of  a 
flush-tank,  can  be  made  effective  through  a  long  stretch  of  sewer. 
The  objections  are  the  trouble  and  the  danger  of  neglect  inherent 
in  hand  work,  and  the  usual  greater  length  of  time  between  flushings. 
To  flush  the  sewers  daily  would  be  very  expensive,  both  as  to  labor 
and  as  to  the  large  amount  of  water  needed. 

Occasionally,  very  favorable  local  circumstances  may  permit  of 
the  admission  at  will  of  large  volumes  of  water  for  flushing  purposes 
from  a  stream  or  lake  higher  than  the  sewer. 

In  some  cases,  hand-flushing  is  done  by  temporarily  damming 
up  the  sewage  itself,  and  then  suddenly  releasing  it  when  sufficient 
head  has  been  secured. 

A  fire  hose  run  to  a  manhole  from  a  nearby  hydrant  may  be  the 
resort  in  other  cases.  In  extreme  cases,  water  has  even  been  hauled 
to  the  sewer  in  tanks,  for  flushing. 

26.  Sewer  Ventilation.     More  fear  used  to  be  felt  of  the  danger 
of  sewer  gas  (more  properly  termed  sewer  air,  see  Art.  1)  in  communi- 
cating disease,  than  medical  knowledge  warrants  at  the  present  time. 
Nevertheless,  it  is  very  important,  not  only  from  the  sanitary  but 
from  many  other  points  of  view,  that  sewer  air  should  be  as  pure  as 
possible;  and  this  requires  good  ventilation  of  the  sewers.     Fresh-air 
currents  in  the  sewers  should  be  maintained  in  some  reliable  way. 

One  method  of  securing  this  is  to  use  perforated  manhole  covers 
(see  Fig.'  9).  Objection  is  sometimes  made  to  these  as  letting  objec- 


SEWERS  AND  DRAINS  29 

tionable  odors  out  into  the  street;  but  with  well-designed  and  well- 
constructed  sewers,  well  flushed  and  well  ventilated,  there  will  be  no 
cause  for  complaint.  If  there  are  seriously  objectionable  odors  from 
the  manholes,  such  odors  should  be  considered  valuable  as  notices 
that  the  sewers  are  in  dangerous  condition,  demanding  immediate 
work  to  make  them  safe.  Sewer  air  escaping  into  streets  through 
manhole-cover  perforations,  is  at  once  so  diluted  by  fresh  air  as  not 
to  be  dangerous  to  the  health  of  passers  by. 

Another  effective  means  for  securing  good  ventilation  is  to 
extend  the  cast-iron  soil-pipes  (which  form  the  main  drainage  pipes 
in  the  plumbing  systems  of  houses)  untrapped  and  full  size  through 
the  roof.  Figs.  4  and  35  show  the  omission  of  traps  on  the  soil  pipe. 
In  Fig.  35,  however,  the  use  of  a  disconnecting  trap,  to  disconnect 
the  sewer  air  from  that  in  the  house  plumbing  pipes,  is  shown  by 
broken  lines.  In  case  this  is  used,  a  ventilating  pipe  for  the  sewer 
should  be  extended  up  the  sides  of  the  house  from  the  sewer  side  of 
the  trap,  and  a  fresh-air  inlet  provided  on  the  house  side,  both  as 
shown  by  the  broken  lines  in  Fig.  35. 

The  use  of  perforated  manhole  covers  and  untrapped  soil  pipes 
extending  through  the  roofs,  is  all  that  is  required  to  secure  good 
ventilation  of  the  sewers,  the  house  connections,  and  the  soil  pipes 
themselves.  Their  use  provides  a  large  number  of  openings  at 
different  levels;  and  the  temperature  of  the  air  in  the  sewers  is  prac- 
tically always  different  from  that  above  the  ground.  Hence  air- 
currents  are  maintained  for  the  same  reason  that  chimneys  cause 
draughts  for  fires,  and  a  good  circulation  of  air  is  maintained. 

In  the  past,  experiments  in  sewer  ventilation  have  been  made 
with  tall  chimneys,  fan  blowers,  etc.;  but  such  devices  are  entirely 
unnecessary,  are  very  costly,  and  are  usually  unsuccessful  on  account 
of  the  very  large  number  of  openings  into  the  sewer,  which  limit 
the  air-currents  produced  by  such  devices  to  short  distances. 

27.  Street  Inlets  and  Catch=Basins.  In  the  case  of  storm  sewers 
and  combined  sewers,  means  must  be  provided  for  admitting  the 
storm  water  to  the  sewers  from  the  streets.  For  this  purpose,  either 
street  inlets,  as  shown  in  Fig.  13,  or  catch-basins,  as  shown  in  Fig.  14^ 
may  be  used.  If  the  water  can  be  allowed  to  flow  one  block  safely 
in  the  surface  gutters,  the  inlets  for  storm  water  would  need  to  be 
only  at  each  street  intersection.  In  a  few  cases  they  need  to  be 


30 


SEWERS  AND  DRAINS 


Curb-1i 

Plan 
Fig.  13.    Street  Inlet. 


closer;  but  in  many  more  cases  the  storm  water  can  be  carried  in  the 
gutters  for  two  or  even  a  greater  number  of  blocks  without  injury, 
thus  greatly  reducing  the  number  and  cost  of  storm  sewers  and  of 
inlets  for  storm  water. 

The  simplest  and  least  expensive  arrangement  for  admitting 
storm  water  is  the  street  inlet,  which,  as  shown  in  Fig.  13,  is  a  mere 
branch  sewer,  with  a  grated  opening  from  the 
street.  Besides  costing  less,  the  street  inlet  is 
often  preferred  for  sanitary  reasons,  as  it  does 
not  retain  foul,  unsanitary  deposits,  as  does  the 
c^tch-basin. 

The  catch-basin,  shown  in  Fig.  14,  is  designed 
to  catch  the  sand,  dirt,  and  other  heavy  street 
detritus,  and  prevent  their  entering  the  sewer. 
Unless  catch-basins  are  frequently  cleaned, 
however  (which  is  very  seldom  the  case),  they 

fail  almost  entirely  in  this;  and  as  they  are  usually  well  filled  with 
more  or  less  foul  deposits,  they  are  condemned  by  many  engineers. 
When  street  inlets  and  catch-basins  are  left  untrapped,  as  shown 
in  Figs.  13  and  14,  they  assist  in  the  ventilation  of  the  sewers.  This 
is  sometimes  objected  to  on  account  of  the  opportunity  for  the  escape 
of  foul  odors,  and  traps  are  introduced  in 
both,  as  shown  by  the  dotted  lines  in  Fig. 
14,  to  prevent  ventilation  of  the  sewers 
through  the  storm  inlets.  If  the  sewers 
are  kept  in  as  good  condition  as  they 
should  be,  there  will  be  no  good  ground  for 
such  objections. 

28.  Inverted  Siphons.  It  sometimes 
becomes  necessary  or  desirable  to  carry 
a  sewer  down  below  the  regular  grade  line, 
to  pass  under  some  obstacle  or  depression, 
and  to  raise  it  again  to  the  regular  grade  line  beyond.  Such  a  stretch 
of  sewer  will  necessarily  flow  full  and  be  under  some  pressure.  It 
is  called  an  inverted  siphon.  The  necessity  for  the  use  of  the  in- 
verted siphon  may  be  occasioned  by  some  stream,  by  railway  tracks, 
by  another  sewer,  by  a  large  water  main,  or  sometimes  merely 
by  a  low  stretch  of  ground  which  happens  to  lie  at  such  a  level 


drat 


Secti  on 


Qratincj* 


Curb -lint 


Fig.  14.    Catch-Basin. 


SEWERS  AND  DRAINS 


31 


that   the  sewer  cannot  be  carried   across  it  at   the   regular  grade. 

Inverted  siphons  have  often  been  constructed  and  operated 
successfully.  It  is  wise,  however,  to  take  certain  precautions  in  their 
design  and  construction,  as  otherwise  serious  trouble  may  be  ex- 
perienced with  them. 

First,  as  to  material,  it  may  be  said  that  ordinary  sewer  pipe  is  not 
well  suited  to  carry  sewage  under  pressure,  on  account  of  the  great 
difficulty  in  making  absolutely  tight  joints,  and  on  account  of  the 
brittle  and  unreliable  nature  of  the  pipe  as  to  resistance  to  bursting 
pressures.  If  used  under  pressure,  pipe  sewers  should  be  subjected  to 
only  a  few  feet  of  head,  and  all  joints  should  be  thoroughly  encased 
in  impervious  Portland  cement  mortar  and  concrete,  reinforced  with 
imbedded  steel  bands.  Brick  masonry  is  still  less  suited  to  with- 


e  :?7??!'?i 


2  Iron  Pipes 


Fig.  15.    Sectional  Elevation  and  Plan  of  Inverted  Siphon. 

stand  bursting  pressures.  '  Ordinarily  iron  pipe  should  be  used  for 
inverted  siphons. 

Second,  it  is  especially  important  to  insure  a  current  in  the 
inverted  siphon  sufficiently  rapid  to  prevent  deposits.  If  the  flow 
is  light  at  first,  to  increase  afterwards,  as  is  often  the  case,  it  is  well 
to  divide  the  siphon  into  two  or  more  pipes  with  valves  on  each,  so 
that  the  entire  flow  can  be  turned  into  one  at  first.  If  it  is  easy  to 
add  the  second  pipe  in  the  future,  it  may  often  be  left  out  at  first. 
Thus  in  Fig.  38,  the  inverted  siphon  from  the  18-inch  outlet  sewer  to 
the  septic  tank  is  at  present  only  an  8-inch  cast-iron  pipe,  with  pro- 
vision for  adding  a  12-inch  cast-iron  pipe  later. 

Third,  the  design  should  be  such  as  to  permit  ready  access  for 
inspection  and  removal  of  obstructions.  The  inverted  siphon  should, 


32  SEWERS  AND  DRAINS 

if  possible,  be  so  planned  that  the  flow  of  sewage  can  be  diverted  for 
a  short  time,  either  into  one  pipe,  or  entirely  away  from  the  siphon ; 
and  the  siphon  should  drain  to  a  low  point  from  which  the  contents 
can  be  removed  by  gravity  through  a  blow-off  or  by  being  pumped  out. 
Where  feasible,  and  especially  where  it  will  be  very  difficult  (as  under 
a  stream)  to  dig  down  to  the  siphon  in  emergencies,  the  siphon  should 
be  made  absolutely  straight  in  grade  and  alignment,  and  a  manhole 
placed  at  each  end. 

In  Fig.  15  is  shown  an  outline  of  an  inverted  siphon  designed 
according  to  the  above  principles. 

Where  the  siphon  can  readily  be  opened  for  repairs,  as  is  the 
case  with  the  one  in  Fig.  38,  such  expensive  construction  need  not  be 
resorted  to.  The  one  in  Fig.  38,  which  carries  sewage  across  low 
ground  to  a  sewage  tank  about  seven  feet  above  the  surface,  is  laid 
at  an  average  depth  of  about  six  feet,  and  neither  the  grade  nor  the 
alignment  is  straight.  It  drains,  however,  to  a  low  point,  where  a 
blow-off  into  a  sewer  is  placed. 

29.  Outlets  for  Sewer  Systems.  We  have  heretofore  discussed 
the  house  connection,  and  the  laterals,  submains,  and  main  sewers, 
with  their  manholes,  flush-tanks,  and  other  accessories.  We  come 
next  to  the  outlet, which,  though  not  considered  first  here,  would  be  one 
of  the  first  things  a  sewerage  engineer  would  have  to  consider  in 
designing  a  sewer  system. 

Where  possible,  all  of  the  sanitary  sewage  or  combined  sewage 
of  the  city  should  be  led  to  one  outlet,  as  the  cost  of  disposing  of  it 
properly  may  be  lightened  thereby,  and  as  the  danger  of  injunction 
suits  and  other  legal  difficulties  arising  from  damages  from  impurified 
or  only  partially  purified  sewage  may  be  multiplied  with  the  number  of 
outlets.  Often  this  will  be  possible  by  constructing  comparatively 
short  lengths  of  deep  sewers  where  at  first  sight  the  topography  would 
seem  to  make  it  impossible  to  secure  one  outlet.  The  size  of  the  city, 
as  well  as  the  topography,  will  affect  the  number  of  outlets. 

Storm  sewage  in  the  separate  system  can  usually  be  discharged 
through  a  number  of  outlets  into  nearby  natural  watercourses. 

Great  effort  should  be  made  to  secure  an  outlet  or  outlets  for  the 
sewer  system  low  enough  to  drain  all  parts  of  the  city  by  gravity. 
Pumping  of  the  sewage  or  a  material  part  of  it,  will  mean  a  con- 
tinuous expense  involving  an  amount  which  would  be  sufficient  to 


SEWERS  AND  DRAINS  33 

pay  the  interest  on  a  large  initial  expense  to  secure  a  gravity  outlet. 
Besides,  there  is  the  danger  of  such  apparatus  failing  at  critical  times. 
Usually  effort  is  made  to  secure,  if  possible,  an  outlet  into  a 
considerable  itream  or  body  of  water,  even  if  the  sewage  is  to  be 
purified. 

30.  Sewage  Disposal.    Heretofore,  sewage  has  been  disposed  of, 
in  the  great  majority  of  cases,  by  simply  emptying  it  into  the  largest 
available  stream  or  body  of   water   near    at   hand.     Such  serious 
contamination  of  natural  waters  has  resulted  from  this  practice,  that 
at  the  present  time  much  more  attention  than  formerly  is  being 
paid  to  sewage  purification ;  and  usually  the  outlet  plans  should  be 
made  with  the  expectation  that  some  method  of  purification  will 
have  to  be  adopted  in  the  future,  if  not  at  present. 

Sewage  disposal  is  discussed  further  on,  at  much  greater  length 
(see  Arts.  110  to  124).  It  will  only  be  said  here  that  the  methods  at 
present  in  favor  almost  all  involve  passing  the  sewage  through  large 
tanks,  and  then  through  some  form  of  filter. 

SEWER  MATERIALS  AND  CROSS=SECTIONS 

31.  Sewer  Materials.     Sewers  24  inches  in  diameter  and  under, 
are  usually  built  of  vitrified  sewer-pipe.     A  24-inch  pipe  sewer,  laid 
to  a  fall  of  0.2  feet  in  100  feet,  will  carry  the  sanitary  sewage,  under 
average  conditions,  of  29,000  people;  and  hence  it  is  evident  that  in 
separate  systems,  all  the  sanitary  sewers  will  be  made  of  pipe,  except 
a  few  main  and  outlet  sewers  in  large  cities.     Considerable  percentages 
of  storm  sewer  and  combined  sewer  systems  will  be  pipe  sewers  also. 

Occasionally  cement  sewer-pipe  is  used  instead  of  the  vitrified 
pipe. 

Sewers  30  inches  and  larger  in  diameter,  are  most  frequently 
built  of  brick.  Pipe  is  sometimes  used,  however,  for  30-inch  to  36- 
inch  sewers. 

Concrete  has  of  late  years  been  growing  in  favor,  to  take  the  place 
of  brick  in  sewer  construction. 

Stone  was  formerly  used  to  a  considerable  extent  for  sewers; 
but  on  account  of  its  roughness,  and  the  great  cost  of  cut-stone 
masonry,  stone  is  suited  only  for  backing  brick  linings  in  larger  sewers, 
Even  here,  concrete  would  now  ordinarily  be  employed,  as  both 
cheaper  and  better. 


34 


SEWERS  AND  DRAINS 


Occasionally,  as  in  the  case  of  submerged-outlet  sewers  into 
bodies  of  water,  or  sewers  across  marshes  on  soft  foundations,  wooden 
stave  pipe  is  used  for  sewers.  These  pipes  are  made  of  pieces  of 
timber,  usually  about  two  inches  by  four  inches  in  size,  put  together 
breaking  joints  in  the  field,  and  hooped  at  regular  intervals  with  iron 
bands  which  can  be  screwed  tight.  Wood  should  be  used  only  where 
it  will  be  wet  all  the  time,  to  prevent  rotting. 

Cast-iron  pipe,  such  as  is  used  for  water  mains,  is  often  adopted 
for  short  stretches  of  sewer  under  railways  or  streams  where  great 
strength  is  essential;  for  inverted  siphons;  and  in  cases  where  abso- 
lutely water-tight  joints  are  essential,  such  as  submerged  lines  in  lakes, 

harbors,  and 
stream  crossings, 
or  where  there  is 
much  ground 
water. 

32.     Vitrified 
Sewer=Pipe.   Vit- 

i  Bend  or  curve  rified  sewer-pipe 
has  many  excel- 
lent qualities  for 
sewer  use.  It  is 
hardjimpervious, 
smooth,  strong, 
does  not  decay 

or  disintegrate,  and  is  not  affected  by  chemicals.  It  has  few  joints 
as  compared  with  brickwork,  and  these  joints  are  of  convenient 
shape  to  make  practically  water-tight.  Vitrified  sewer-pipe  is  readily 
handled  and  laid  in  sewer  construction.  The  materials  of  which  it  is 
made  are  widely  distributed,  and  hence  the  cost  of  the  pipe  is 
reasonable. 

In  Fig.  16  are  shown  the  general  forms  of  the  straight  pipe  and 
also  of  the  special  fittings  (sewer-pipe  specials)  most  commonly  used 
in  sewer  construction. 

In  Table  I  (page  35)  are  given  standard  dimensions  for  straight 
sewer-pipe. 

Vitrified  sewer-pipe  is  made  from  shale  clays,  in  very  much  the 
same  way  as  brick  and  other  clay  products.  The  temperature  at 


DoUble -Y 


Double  -T 


D» 


Cvirve  Reducer  Increase]- 

Fig.  16.    Vitrified  Sewer-Pipe  and  Specials. 


SEWERS  AND  DRAINS 


35 


which  it  is  burned  in  the  kilns  must  be  very  high,  as  in  the  case  of 
paving  brick,  so  as  to  produce  an  "incipient  vitrification,"  a  softening 
and  running  together  of  the  particles  of  clay,  which  gives,  on  cooling, 
a  very  hard,  impervious,  and  strong  structure.  Smoothness  of 
interior  and  exterior  surfaces  is  secured  by  the  use  of  salt  during  the 
process  of  burning,  so  as  to  produce  a  " salt-glazed,"  glassy  skin. 

TABLE  I 
Standard  Dimensions  for  Sewer  Pipe 


STANDARD 

DOUBLE  STRENGTH  OR   EXTRA 
THICK 

INSIDE 

THICKNESS 

DEPTH  OF 

WEIGHT 

INSIDE 

THICKNESS 

DEPTH  OF 

WEIGHT 

DlAM. 

OF    SHELL. 

SOCKET. 

PER    FT. 

DlAM. 

OF    SHELL. 

SOCKET. 

PER  FT. 

INCHES 

INCHES 

INCHES 

LBS. 

INCHES 

INCHES 

INCHES 

LBS. 

8 

| 

2* 

22 

8 

* 

24 

25 

9 

2i 

27 

9 

1 

2* 

30 

10 

| 

2| 

30 

10 

1 

2* 

34 

12 

2J 

41 

12 

H 

3 

50 

15 

;  |. 

3 

60 

15 

It 

3 

70 

18 

£ 

3 

80 

18 

3 

100 

20 

a. 

3 

95 

20 

if 

3 

120 

21 

| 

4 

105 

21 

if 

4 

140 

24 

If 

4 

135 

24 

2 

4 

180 

27 

2 

4 

215 

27 

2i 

4 

240 

30 

2i 

4 

270 

30 

2| 

4 

300 

33 

2f 

4* 

320 

33 

2f 

4* 

340 

36 

2* 

5 

365 

36 

2f 

5 

390 

The  bells  are  made  large  enough  to  allow  an  annular  space  for  cement, 
ranging  from  f  inch  thick  for  8-inch  pipe  to  f  inch  for  36-inch  pipe. 
Smaller  sizes  of  pipe,  down  to  3  inches  in  diameter,  are  made. 
Double-strength  pipe  is  used  only  in  cases  requiring  unusual  strength. 

Vitrified  sewer-pipe  must  be  carefully  inspected,  piece  by  piece, 
just  before  being  used  in  the  sewer,  all  poor  material  being  rejected. 
Some  of  the  points  to  be  noted  in  making  the  inspection  are  as  follows : 

(1)  The  pipe  should  be  straight,  and  true  in  shape. 

(2)  The  pipe  must  have  a  hard-burned,  strong  internal  structure 
showing  incipient  vitrification.     Small  pieces  may  be  chipped  out  of 
occasional  lengths  to  test  this;  and  the  color  will  also  be  a  guide 
after  the  inspector  has  become  thoroughly  familiar  with  the  make 
of  pipe  being  used. 

(3)  The  hub  and  socket  ends  of  adjacent  pipes  should  fit  to- 
gether well,  leaving  at  least  the  spaces  for  cement  given  under  Table  I. 

(4)  There  must  not  be  on  the  lower  half  of  the  interior  of  the 
sewer  any  lumps,  blisters,  or  excrescences.    A  few  may  be  allowed, 


36  SEWERS  AND  DRAINS 

if  not  too  large,  if  the  pipe  can  be  turned  so  as  to  bring  them  to  the 
upper  half. 

(5)  There  must  be  no  cracks  extending  into  the  body  of  the  pipe, 
or  of  such  nature  as  to  weaken  it  materially.     On  tapping  the  pipe 
with  a  light  hammer,  if  it  does  ftot  give  a  clear  ring,  the  presence  of 
invisible  cracks  may  be  suspected. 

(6)  There  must  be  no  broken  pieces  of  material  size,  from 
either  the  hub  or  the  socket  ends,  nor  any  at  all  which  cannot  be 
turned  to  the  upper  half. 

Nothing  of  human  construction  can  be  perfect,  and  sewer  pipes 
are  no  exception  to  the  rule.  Hence  the  pipe  inspector  must  have 
good  judgment  and  considerable  experience  to  draw  the  line  prop- 
erly between  important  and  unimportant  defects.  In  clause  25,  Art. 
93,  of  the  sewer  specifications  given  hereinafter,  some  definite  rules  are 
laid  down  to  govern  inspectors  in  this  particular. 

Vitrified  pipe  can  be  secured  in  2,  2J,  and  3-foot  lengths.    The 

longer  the  lengths,  the  fewer  the  joints,  which  is  a  material  advantage. 

33.    Joints  in  Pipe  Sewers.    The  joints  are  the  weakest  points 

in  pipe  sewers,  and  should  be  made  with  the  utmost  pains  to  secure  as 

nearly    as   practicable    an   absolutely 
t  Mortar      water-tight  job.     In  Fig.  17,  the  upper 
joint  shown  illustrates  the  form  com- 
monly  employed. 

Ordinary  Joint 

In  the  bottom  of  the  trench,  which 

^rya- Cerne vit  Mortar 

should  be  rounded  to  fit  the  under  part 
°f  tne  sewer  pipe,  bell-holes  are  dug  for 

Fig.  17.  joints  in  pipe  Sewers,  all  bells,  to  permit  the  joint  on  the  un- 
der side  of  the  pipe  to  be  made  prop- 
erly, and  to  give  the  pipe  a  bearing  on  its  full  length  instead  of 
merely  on  the  bells.  Before  the  spigot  end  of  the  pipe  to  be  laid 
is  entered  .into  the  bell  of  the  last  pipe  laid,  it  should  be  wrapped' 
with  a  gasket  of  hemp,  oakum,  or  jute,  as  shown  in  Fig.  17,  so 
that  the  inverts  of  the  two  pipes  will  match  in  a  smooth  line  when 
the  pipe  is  entered,  and  so  as  to  prevent  the  soft  cement  mortar 
from  bemg  forced  up  through  the  joint  to  project  into  the  pipe.  The 
gasket  also  assists  in  making  the  joint  water-tight,  especially  if  there 
is  water  in  the  trench.  Disastrous  results  have  often  followed  the 
omission  of  the  gasket,  which  should  always  be  used. 


SEWERS  AND  DRAINS  37 

After  the  pipe  is  entered  and  brought  exactly  to  grade,  Portland 
cement  mortar,  mixed  about  1  to  1  or  1  to  2  with  sand,  should  be 
calked  into  the  joint,  to  fill  it  absolutely  full,  and  should  be  beveled 
off  on  the  outside,  as  shown  in  the  figure.  Special  care  should  be 
taken  on  the  under  side  of  the  pipe.  Immediately  after  placing  the 
cement,  the  bell-hole  should  be  packed  full  of  sand,  so  as  to  support 
the  cement  on  the  under  side  of  the  pipe  till  it  has  set.  It  is  best  to 
keep  the  cementing  back  two  or  three  lengths  of  pipe  from  the  pipe 
laying,  to  avoid  danger  of  the  cement  being  broken  in  placing  the  next 

pipe- 
Without  the  most  careful  watching  of  every  joint  during  con- 
struction, the  workmen  are  sure  to  slight  the  joints.     An  inspector 
should  be  kept  constantly  on  the  work. 

In  the  lower  part  of  Fig.  17  is  shown  the  ring  joint,  formerly  pre- 
ferred by  some  engineers,  but  now  very  seldom  used.  It  is  more 
costly  than  the  ordinary  form. 

Various  joints  have  been  invented  and  used  to  a  limited  extent, 
which  include  simple  beveling  of  the  ends  of  the  pipe  without  using 
bells,  the  use  of  grooves  at  one  end  with  corresponding  projections 
at  the  other  end,  etc.  Sometimes  the  exterior  of  the  spigot  end  and 
the  interior  of  the  bells  are  grooved  and  made  rough  in  the  ordinary 
form  of  joint.  This  is  an  advantage  in  holding  the  cement,  and  in 
securing  a  water-tight  job. 

34.  Cement  Sewer-Pipe.  Ever  since  the  early  use  of  pipe  sewers 
in  the  latter  half  of  the  nineteenth  century,  cement  pipe  has  been  used 
to  some  extent  for  sewers;  and  recently  there  seems  to  be  a  revival 
and  extension  of  its  use.  Experience  has  shown  that  cement  is  a  very 
suitable  material  for  making  sewer  pipe,  and  that  cement  pipes, 
when  well  made,  of  first-class  materials,  give  excellent  satisfaction 
for  sewers,  and  are  durable  and  not  disintegrated  by  the  sewage. 
The  manufacture  of  good  cement  sewer-pipe,  however,  cannot 
be.  successfully  carried  on  by  men  who  do  not  have  the  necessary 
skill,  which  is  to  be  gained  only  by  experience  in  this  particular  work; 
and  even  skilled  manufacturers  will  not  be  successful  unless  both  the 
cement  and  the  sand  used  are  of  first-class  quality,  nor  unless  plenty  of 
cement  is  used.  Much  poor  cement  pipe  has  been  made,  because 
these  almost  self-evident  facts  have  not  been  understood ;  and  in  this 
way  cement  sewer-pipe  has  gained  a  bad  reputation  in  many  localities. 


38 


SEWERS  AND  DRAINS 


In  general  it  may  be  said  that  the  sand  should  be  clean/  sharp, 
and  coarse,  and  that  it  should  contain  a  considerable  proportion  of 
fine  pebbles,  smaller  than  a  cherry-pit.  Only  the  best  Portland  cement 
should  be  used,  and  the  mortar  should  not  be  weaker  than  1  to  3. 
The  mixing  must  be  very  thorough,  as  also  the  tamp- 
ing into  the  moulds. 

Two  general  kinds  of  cement  sewer-pipe  are  made. 
In  one,  just  coming  into  use,  the  pipes  are  made  con- 
tinuously in  the  ditch.  A  form  of  moulds  is  used  to 
Fie.  is.  circular  ^ve  *ne  correct  shape  and  size,  which  can  be  forced 
FngersoneRun',  ahead  as  the  work  progresses;  and  there  are  no  joints. 
'  ioewa.  °  es>  It  is  too  soon  yet  to  tell  how  successful  this  plan  may  be. 
In  the  more  common  form  of  cement  sewer-pipe,  the 
pipes  are  made  in  a  factory,  in  pieces  of  the  same  length  as  vitrified 
pipe.  Usually,  comparatively  little  water  is  used  in  mixing,  in  order  to 
permit  immediate  removal  of  the  pipe  from  the  moulds. 
While  such  pipe  are  curing  (setting),  the  omitted  water 
must  be  supplied  by  frequently  wetting  them,  or  the 
process  of  setting  and  hardening  cannot  go  on  properly. 
Many  cement  sewer-pipes  of  this  kind  are  spoiled  in  the 
curing.  Fig.  19. 

•  •    •  Egg -Shaped 

Cement  pipe  are  now  made  with  bells  tor  the  noints,  Brick   com- 

*  '    bined  Sewer. 

the  same  as  vitrified  pipe.     The  manufacture  of  specials, 
such  as  the  Y-junctions  required  in  such  numbers  for  house  connec- 
tions, is  still  in  unsatisfactory  condition. 


L12  Pipe 

Fig.  20.    Circular  Brick  Sewer  with  Sub- 
drain,  64th  Street.  Brooklyn,  N.  Y. 


Fig.  21.    Section  of  a  Large  Sewer  in 
St.  Louis,  Mo. 


The  body  of  a  cement  sewer-pipe  is  of  much  weaker  material 
than  that  of  which  vitrified  pipe  are  made;  and  the  thickness  of  cement 
pipe  should  be  much  greater  than  the  thickness  given  in  Table  I  for 
vitrified  pipe. 


SEWERS  AND  DRAINS 


39 


35.  Typical  Cross=Sections  of  Large  Sewers.  In  Figs.  18  to 
25,  inclusive,  are  shown  some  typical  designs  for  sewers  too  large  to 
be  constructed  of  sewer  pipe. 

In  Fig.  18,  the  common  circular  form  is  shown.  This  form  is 
more  economical  to  construct  than  any  other  when  good  foundations 


Fig.  22.    Ingersoll  Run  Sewer  with  Low 
Headroom,  Des  Moines,  Iowa. 


Fig.   23     Dry-Run  Sewer, 
Waterloo,  Iowa. 


can  be  had,  for  the  circle  gives  a  larger  area  and  velocity  of  flow  when 
full  than  any  other  shape  having  the  same  circumference. 

In  the  case  of  combined  sewers,  however,  the  dry-weather  flow 
of  sewage  is  so  very  small,  in  comparison  with  the  size  of  the  sewer, 
that  it  makes  only  a  shallow,  trickling  stream  of  little  velocity,  and  the 
sewer  will  not  be  self-cleansing.  For  such  sewers,  this  difficulty  can 
be  overcome  by  the  use  of  the  egg-shape  of  sewer,  shown  in  Fig.  19. 
This  shape  has  a  circular  inv  rt  having  a  radius  only  half  that  of  the 
top;  and  the  depth  and  velocity  of  the  dry-weather  flow  will  be  the 
same  as  in  a  circular  sewer  of  this  smaller  radius,  while  at  the  same  time 
the  capacity  in  time  of  flood  is  equivalent  to  a  much  larger  circle. 

In  Fig.  20,  a  favorite  type  of  design  for  very  large  circular  sewers 


Fig.  24.    Old  Type  of  Main  Sewers, 
Paris,  France. 


Fig.  25.    New  Type  of  Sewers, 
Paris,  France. 


is  shown.  For  such  large  sewers,  the  upper  half  constitutes  an  arch, 
which  exerts  heavy  pressures  or  thrusts  horizontally  outward  against 
the  sides  of  the  sewer  at  the  height  of  the  center.  To  withstand  these 
thrusts,  the  masses  of  masonry  backing  shown  in  the  figure  are  added. 
This  backing  may  be  of  brick,  rubble-stone,  or  concrete  masonry. 


40  SEWERS  AND  DRAINS 

In  the  large  sewers,  too,  it  usually  is  not  practicable  to  round  the 
bottom  of  the  trench  to  fit  the  circular  shape,  as  is  done  for  smaller 
sewers;  and  hence  the  flat  foundation,  also  shown  in  the  figure,  is 
adopted.  In  soft  materials,  it  often  becomes  necessary  to  drive  piles 
to  carry  the  weight  of  sewers. 

In  Fig.  21  is  shown  the  favorite  design  for  large  sewers.  For 
reasons  given  in  discussing  Fig.  20,  the  foundation  is  necessarily 
made  flat;  and  with  this  shape  of  foundation,  Fig.  21  will  give  a 
larger  area  and  capacity  for  the  same  amount  of  material  than  Fig.  20, 
other  conditions  being  the  same.  Also,  Fig.  21  requires  less  head- 
room than  Fig.  20  for  the  same  capacity — which  is  often  of  great 
importance  in  the  case  of  these  large  sewers.  The  invert  of  Fig.  21 
is  not  so  well  suited  to  prevent  deposits  as  that  of  Fig.  20;  but  in  the 
case  of  these  large  sewers,  there  is  usually  a  large  flow  even  in  dry 
weather,  so  that  this  point  may  be  of  little  importance. 

In  Fig.  23  we  have  an  example  of  the  use  of  concrete  for  a  large 
sewer  of  the  general  type  shown  in  Fig.  21,  and  just  discussed. 

In  Fig.  22  we  have  an  extreme  case  of  low  headroom,  secured  by 
making  the  top  an  absolutely  flat  slab  of  concrete,  reinforced  with 
steel.  In  this  case  the  bottom  of  the  sewer  was  necessarily  located 
at  a  very  shallow  depth  below  the  street,  while  the  required  size  of 
sewer  was  large. 

Finally,  in  Figs.  24  and  25,  are  shown  two  typical  cross-sections 
of  the  famous  sewers  of  Paris.  The  large  main  shown  in  Fig.  24  acts 
not  only  as  a  sewer,  but  also  as  a  subway  for  the  water  mains  and  for 
other  purposes.  The  entire  ordinary  flow  of  sewage  is  confined 
within  the  cunette,  or  comparatively  small  channel  shown  in  the 
bottom.  The  ledge  on  each  side  serves  for  the  passage  of  workmen 
and  of  cleaning  carts,  flushing  devices,  etc.  The  section  shown  in 
Fig.  25  is  a  later  type,  and  is  more  nearly  self-cleansing.  The  dirt 
in  the  streets  is  washed  into  these  sewers  by  the  use  of  hose,  and 
special  conveniences  for  cleaning  it  out  of  the  sewers  are  needed. 

36.  Junction=Chambers  for  Large  Sewers.  Where  two  or 
more  large  sewers  join,  special  difficulties  present  themselves,  in 
providing  supports  for  the  partial  arches  whose  supports  are  cut 
away  in  making  the  junction.  It  is  usually  necessary,  when  the 
sewers  are  large,  to  build  a  masonry  chamber  enclosing  the  entire 
junction,  and  with  a  self-supporting  roof  spanning  all  the  sewers. 


SEWERS  AND  DRAINS 


41 


Various  designs  for  such  junction-chambers  are  used,  but  the 
most  common  type  is  illustrated  in  Fig.  26.  Here  a  bell-mouth  arch  is 
used  to  span  the  opening,  the  case  being  the  junction  of  three  of  the 
Chicago  intercepting  sewers  (see  Fig.  5).  Sometimes  flat  roofs  are 
used,  supported  by  steel  beams  or  made  of  reinforced  concrete. 

The  bottoms  of  such  junctions  are  the  mathematical  inter- 
sections, executea  in  masonry,  of  the  lower  halves  of  the  sewer  chan- 
nels; and  for  sewers  not  too  large,  the  upper  halves  may  sometimes 
be  built  in  a  similar  way, 
or  with  vault  ribs,  as  in 
the  roofs  of  old  cathe- 
drals. 

37.  Brick  Sewers. 
It  has  already  been  stated 
that  brick  is  the  favorite 
material  for  sewers  too 
large  to  be  made  of  pipe, 
the  dividing  line  usually 
being  drawn  at  30  inches 
to  36  inches  diameter. 
Brick  present  many  ad- 
vantages for  sewer  work, 
including  their  moderate 
cost,  their  durability,  and 
their  small  size  and  reg- 
ular shape,  which  enable 
them  to  be  readily  han- 
dled and  used  in  building  sewers  of  any  desired  cross-section,  with 
comparatively  smooth  and  true  interior  surfaces. 

Sewer  brick,  as  those  suitable  for  sewer  construction  are  commonly 
called,  should  be  harder  burned  than  ordinary  building  brick,  to 
enable  them  to  stand  the  wear  from  the  flow  of  sewage,  and  to  insure 
against  disintegration.  They  need  not,  however,  be  as  hard  burned 
as  No.  1  paving  brick,  and  hence  constitute  an  intermediate  grade 
between  building  brick  and  pavers.  Sewer  brick  should  be  uniform 
in  size,  and  of  regular,  true  shape,  so  as  to  permit  of  being  laid  with 
thin  joints,  to  form  smooth,  true  surfaces.  They  should  be  carefully 
inspected  on  the  work  just  before  being  used,  and  all  defective  brick 


Plan  of  Chamber* 


Fig.  26.    Junction   of  Brick   Sowers,  Lawrence  and 
Sheridan  Avenues,  Chicago,  111. 


42  SEWERS  AND  DRAINS 

thrown  out.  The  common  size  for  sewer  brick  approximates  8J  by 
4  by  2J  inches. 

-In  the  sewer,  the  brick  are  laid  in  rings,  as  shown  in  Figs.  18  and 
19,  with  the  4-inch  dimension  radial  and  the  8J-inch  dimension  length- 
wise of  the  sewer.  Care  should  be  taken  to  break  joints  in  each  ring. 
The  brick  should  be  laid  in  Portland  cement  mortar,  made  of  at 
least  1  part  of  cement  to  3  parts  of  clean,  sharp  sand  of  medium-sized 
grains.  Pebbles  should  be  screened  out  of  the  sand  so  as  to  permit 
thin  joints.  All  joints  should  be  rilled  full  of  mortar,  the  brick  being 
laid  with  shove  joints,  to  make  a  practically  water-tight  job.  The 
outside  ring  of  the  invert  should  be  laid  against  a  layer  of  1  to  2  Port- 
land cement  mortar;  and  the  outside  of  the  arch  (or  upper  half  of  the 
sewer)  should  be  plastered  with  the  same  mortar,  to  keep  out  ground 
water.  Similarly,  to  prevent  leakage  of  sewage,  the  entire  interior 
surface  of  the  sewer  should  be  plastered  with  the  same  mortar,  or  else 
thoroughly  washed  with  at  least  two  coats  of  liquid  cement,  after 
the  joints  have  been  carefully  pointed  and  smoothed.  Even  with  the 
utmost  care,  it  will  be  found  impossible  to  secure  absolute  water- 
tightness;  and  the  difficulties  will  be  especially  great  when  ground 
water  and  soft  materials  are  encountered  in  the  trench. 

Up  to  6  or  7  feet  diameter,  two  rings  of  brick  are  usually  suffi- 
cient. In  fact,  for  the  smaller  sizes  of  brick  sewers,  one  ring  would 
be  amply  strong  with  firm  foundations;  but  it  is  difficult  to  make  the 
sewer  sufficiently  tight  when  only  one  ring  is  used,  because  all  joints 
extend  entirely  through.  Sometimes  an  exterior  layer  of  concrete 
may  be  used  to  meet  this  objection,  at  least  for  the  lower  half  of  the 
sewer;  or  an  outside  ring  of  brick  may  be  used  for  the  invert  only. 
Sewers  larger  than  6  or  7  feet  in  diameter  usually  require  three  rings 
of  brick;  and  more  are  needed  for  very  large  sewers,  for  which  the 
number  required  must  be  calculated  for  each  particular  case  to  suit 
the  special  conditions. 

38.  Concrete  Sewers.  Of  late  years,  concrete  has  frequently 
been  employed  in  preference  to  other  kinds  of  masonry  for  many 
purposes,  of  which  sewer  construction  is  one.  Its  advantages  for  sew- 
ers are  many.  The  following  may  be  mentioned : 

First,  and  foremost,  the  cost  is  usually  less  than  the  cost  of  brick 
masonry. 


SEWERS  AND  DRAINS  43 

Second,  the  concrete  exactly  fits  the  irregularities  of  the  exca- 
vation, giving  better  foundations. 

Third,  sewers  built  of  concrete  constitute  a  solid  structure  without 
joints,  and  hence  are  less  liable  to  uneven  settlement. 

Fourth,  there  are  no  joints,  as  in  brickwork,  to  be  made  water- 
tight, though,  on  the  other  hand,  it  is  not  easy  to  make  the  body  of  the 
concrete  entirely  impervious  to  seepage. 

Fifth,  the  concrete  can  be  readily  moulded  to  any  desired  shape 
of  sewer. 

Sixth,  the  concrete  can  be  made  by  comparatively  unskilled 
workmen,  if  skilled  foremen  are  employed. 

Concrete  may  be  used  for  foundations,  as  shown  in  Figs.  20  and 
21;  for  the  backing  of  brick  sewer  rings;  and  in  various  other  com- 
binations with  brick;  or  it  may  be  used  for  the  entire  sewer,  as  in 
Figs.  22  and  23. 

Reinforced  concrete,  or  concrete  reinforced  with  steel  rods,  to 
prevent  cracks  from  tension  stresses,  has  opened  up  of  late  years 
entirely  new  possibilities  in  sewer  construction,  of  which  Fig.  22  is 
an  example. 

It  has  been  reported  that  the  concrete  invert  of  the  large  St. 
Louis  sewer  shown  in  Fig.  21  has  shown  surface  pitting  and  dis- 
integration from  the  effects  of  the  sewage.  This  is  a  trouble  which 
does  not  appear  to  have  been  experienced  elsewhere,  and  hence  is 
presumably  uncommon,  and  would  seem  due  most  probably  to  poor 
materials  or  poor  workmanship.  Danger  from  this  source  could  be 
prevented  by  lining  the  concrete  sewer  with  one  ring  of  vitrified 
paving  brick. 

FORMULAE  AND  DIAGRAMS  FOR  COMPUTING  FLOW 

IN  SEWERS 

\ 

39.  Formulae  for  Computing  Flow  in  Sewers.  It  has  already 
been  stated  that  more  than  99 . 8  per  cent  of  even  sanitary  sewage  is 
simply  ordinary  water  which  has  been  added  to  the  foul  wastes  to 
assist  in  removing  them.  Hence  the  mathematical  formulae  for  the 
flow  of  sewage  are  the  same  as  those  for  the  flow  of  water.  They  may 
be  studied  in  detail  in  the  instruction  paper  on  Hydraulics. 

Two  general  hydraulic  formulae  have  commonly  been  employed 
in  sewer  computations,  as  follows: 


44  SEWERS  AND  DRAINS 

(1)     Weisbach's  Formula.     The  older  computations  were  gener- 
ally based  on  Weisbach's  formula,  which  is  as  follows : 


In  the  above  formula, 

v   --  --   Average  velocity  of  flow,  in  feet  per  second. 

</   =   Acceleration  due  to  gravity  =  32 . 2  ft.  per  second. 

h  =   Fall  of  sewer,  in  feet. 

e    =    Coefficient  of  entrance  =  0.505.  n  016Q 

c    =   Coefficient  of  friction  in  pipe  =  0.0144  +  - 

I/   t? 

/    =   Length  of  pipe,  in  feet. 

d  —   Diameter  of  pipe,  in  feet. 

Weisbach's  formula  has  been  much  used  for  sewer  computations, 
for  the  reason  that  Mr.  Baldwin  Latham,  in  the  first  treatise  on  Sani- 
tary Engineering  worthy  the  name  (1873),  published  extensive  tables 
of  flow,  calculated  from  this  formula,  which  made  sewer  computa- 
tions very  simple.  Hence  it  was  easier  for  later  engineers  simply  to 
make  use  of  these  tables  than  to  compute  new  ones  of  their  own. 

(2)  Kutter's  Formula.  In  later  hydraulic  computations,  it 
has  generally  been  considered  that  Kutter's  formula  gives  the  most 
reliable  results.  It  is  as  follows: 

f  41.68 +LSL+    :°°*M 


.66  +  JW*y»     I 

*          /A//2   J 


In  this  formula, 

v    —  Average  velocity  of  flow,  in  feet  per  second. 

R  =  Mean  hydraulic  radius  in  feet  =  Area  of  cross-section  of  stream  in 
square  feet,  divided  by  wetted  perimeter,  in  feet,  of  length  of  portion  of.  cir- 
cumference of  channel  wet  by  the  stream.  (NOTE. — For  circular  pipe  sewers, 
R  =  \  of  the  diameter  when  the  pipe  is  flowing  either  full  or  half -full.) 

S  —  Slope  of  the  sewer  =  •= -r-  • 

n  =  Coefficient  of  roughness,  varying  with  the  roughness  of  the  channel. 

For  pipe  sewers  it  is  common  to  assume  that  n  =  0.013;  and  for  brick 
sewers,  that  n  =  0.015.  For  cement  pipe  sewers,  the  roughness  might  be 
considered  intermediate  between  these  values  of  n;  but  n  =  0.013  is  generally 
used  for  them  as  well  as  for  clay  pipe.  New  and  perfectly  clean  channels 


SEWERS  AND  DRAINS  45 

would  not  be  so  rough  as  indicated  by  these  numbers;  but  the  growths  and 
deposits  which  may  accumulate  in  sewers  render  it  wise  to  adopt  the  above 
values  for  n. 

Both  the  above  sewer  formulae  give  merely  the  average  veloc- 
ities (v)  of  flow.  To  obtain  the  discharge  in  cubic  feet  per  second, 
we  must  multiply  "v"  by  the  area  in  square  feet  of  the  cross-section  of 
the  stream  of  sewage. 

Kutter's  formula  gives  less  capacities  for  pipe  sewers  than  Weis- 
bach's  for  the  small  sizes,  up  to  about  18  inches'  diameter.  It  will 
be  on  the  safe  side  to  adopt  Kutter's  formula;  and  this  is  now  very 
generally  done,  though  actual  gaugings  of  small  pipe  sewers  either 
new  or  in  very  good  condition,  may  often  show  greater  velocities  and 
capacities  than  the  formula  would  indicate,  when  the  values  of  n 
above  given  are  adopted. 

In  this  paper,  Kutter's  formula  will  be  adopted  as  the  basis  of 
all  calculations  of  the  flow  of  sewers. 

40.  Diagram  of  Discharges  and  Velocities  of  Circular  Pipe 
Sewers  Flowing  Full.  Direct  numerical  computations  of  flow  in 
sewers  from  the  formulae  given  above,  would  be  very  laborious  and 
tedious.  The  work  may  be  very  greatly  simplified  by  the  use  of 
tables  or  diagrams.  Diagrams  are  more  convenient  than  tables,  and 
are  adopted  for  this  paper.  With  their  aid,  computations  of  flow 
in  sewers  are  very  easy  and  short. 

Fig.  27  is  such  a  diagram,  giving  the  capacities  and  velocities  of 
circular  vitrified  pipe  sewers  flowing  full.  Cement  pipe  sewers  would 
probably  have  discharges  and  velocities  somewhat  less  than  those 
shown  in  this  figure. 

TO  USE  THE  DIAGRAM 

(A}  When  the  diameter  of  the  pipe  and  the  grade  are  given,  to  find  the 
discharge  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  grade  is  found,  inter- 
polating by  t  he  eye,  if  necessary,  between  the  grades  marked  on  the  diagram. 
(2)  Find  the  point  where  the  vertical  line  through  the  given  grade  intersects 
the  inclined  line  marked  with  the  given  diameter  of  sewer.  (3)  Trace  hori- 
zontally through  this  point,  interpolating  by  the  eye,  if  necessary,  between 
the  horizontal  lines  on  the  diagram ;  and  read  the  discharge  of  the  pipe  running 
full,  on  the  left  side  of  the  diagram  in  cubic  feet  per  second,  or  on  the  right  side 
of  the  diagram  in  gallons  per  24  hours.  (4)  If  the  velocity  is  desired,  it  can 
be  determined  by  noting  where  the  point  (found  in  2,  above)  of  intersection 
of  the  given  grade  and  diameter  lines  falls  with  reference  to  the  inclined  lines 
marked  with  the  different  velocities,  estimating  by  the  eye  the  decimals  of  a 
foot  per  second. 


46 


SEWERS  AND  DRAINS 


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Grades  l-nPerCent=Fefet  Fall 


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Fig.  27. 


Discharges  and  Velocities  of  Circular  Vitrified  Pipe  Sewers  Flowing  Full. 
By  Kutter's  Formula  («,=0.013). 


(B)  When  the  grade  and  the  required  discharge  are  given,  to  find  the  neces- 
sary diameter  of  pipe,  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  given  grade  is  found, 
interpolating  by  the  eye,  if  necessary,  between  the  grades  marked  on  the 
diagram.,  (2)  Find  the  intersection  of  the  vertical  line  through  this  grade 
with  the  horizontal  line  through  the  given  discharge,  finding  the  discharge  on 
the  left  of  the  diagram  if  it  is  given  in  cubic  feet  per  second,  or  on  the  right 
if  it  is  given  in  gallons  per  24  hours.  (3)  Note  between  which  two  diameter 
lines  this  point  of  intersection  falls,  and  take  the  diameter  line  nearest  as  that 
required.  (4)  Also  note  the  position  of  the  point  of  intersection  with  refer- 
ence to  the  velocity  lines,  and  so  estimate  the  velocity,  interpolating  by  the 
eye  between  the  inclined  velocity  lines. 

'((7)  When  the  velocity  and  diameter  are  given,  to  find  the  grade  and  dis- 
charge. 

(1)  Find  the  intersection  of  the  given  diameter  line  with  the  given 
velocity  line,  interpolating  by  the  eye,  if  necessary.  (2)  Then  vertically 
downward  to  the  bottom  of  the  diagram  from  this  point  of  intersection,  read 
the  required  grade;  and  horizontally  to  the  left  side  or  to  the  right  side  of  the 
diagram,  read  the  discharge,  interpolating  by  the  eye  in  each  case,  if  necessary. 
All  other  cases  may  be  solved  by  similar  obvious  methods. 


EXAMPLES 

Example  1.     What  will  be  the  discharge  and  velocity  of  a  15-inch 
pipe  sewer  laid  to  a  0  .  2  per  cent  grade  ? 


SEWERS  AND  DRAINS  47 

Solution.  See  A,  above.  From  the  intersection  of  the  vertical 
0.2  per  cent  grade  line  with  the  inclined  15-inch  diameter  line,  we  read 
horizontally  to  the  left  the  discharge  of  2.8  cu.  ft.  per  second,  or  to  the 
right,  of  1,850,000  gallons  per  24  hours.  We  further  note  that  the  point 
of  intersection  of  the  0.2  per  cent  grade  line  with  the  15-inch  diameter 
line  falls  between  the  2 . 0  and  the  2.5  ft.  per  second  velocity  lines,  and 
by  the  eye  we  estimate  the  velocity  to  be  2.3  ft.  per  second. 

Example  2.  See  B,  above.  What  size  of  pipe  sewer  laid  at  a  grade 
of  0 . 5  per  cent  will  be  required  to  carry  an  average  flow  of  200,000  gallons 
of  sewage  per  day,  the  maximum  rate  of  discharge  being  three  times  the 
average?  (NoTE. — rHence  use  600,000  gallons  discharge  in  solving  the 
example.)  Also,  what  will  be  the  velocity? 

Answer.  Required  diameter  of  sewer,  9  inches;  velocity  of  flow, 
about  2.3  ft.  per  second. 

Example  3.  See  (7,  above.  If  the  minimum  allowable  velocity  of 
flow  is  2  ft.  per  second  when  a  sewer  flows  full,  what  minimum  grade  will 
be  required  to  produce  this  velocity  in  a  12-inch  sewer? 

Answer.     0.23  per  cent  minimum  grade. 

Example  4.  If  an  outlet  sewer  serves  20,000  people,  each  person 
contributes  100  gallons  per  day,  and  the  maximum  rate  of  flow  is  3  times 
the  average,  what  size  of  sewrer  will  be  required,  if  its  grade  is  0 . 25  per 
cent? 

Answer.     24  inches  diameter. 

Example  5.  If  an  8-inch  pipe  sewer  is  laid  at  a  0.45  per  cent 
grade,  what  will  be  the  discharge  and  the  velocity  when  it  flows  full? 

Answer.     480,000  gallons  per  day;  2.1  ft.  per  second. 

Example  6.  A  storm  pipe  sewer  drains  10  acres,  and  should  be 
able  to  carry  1.5  cu.  ft.  per  second  per  acre.  Its  grade  is  0 . 5  per  cent. 
What  diameter  will  be  required  ? 

Answer.     24  inches  diameter. 

41.  Diagram  of  Discharges  and  Velocities  of  Circular  Brick 
and  Concrete  Sewers  Flowing  Full.  Fig.  28  is  the  diagram  for  circu- 
lar brick  and  concrete  sewers,  corresponding  to  Fig.  27  for  pipe  sewers , 
and  is  used  in  the  same  way. 

TO  USE  THE  DIAGRAM 

(A)  When  the  diameter  of  the  pipe  and  the  grade  are  given,  to  find  the 
discharge  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  grade  is  found,  inter- 
polating by  the  eye,  if  necessary,  between  the  grades  marked  on  the  diagram. 
(2)  Find  the  point  where  die  vertical  line  through  the  given  grade  intersects 
the  inclined  line  marked  with  the  given  diameter  of  sewer.  (3)  Trace  hori- 


48 


SEWERS  AND  DRAINS 


zontally  through  this  point,  interpolating  by  the  eye,  if  necessary,  between 
the  horizontal  lines  on  the  diagram ;  and  read  the  discharge  of  the  pipe  runn  ng 
full,  on  the  left  side  of  the  diagram  in  cubic  feet  per  second,  or  on  the  right 
side  of  the  diagram  in  gallons  per  24  hours.  (4)  If  the  velocity  is  desired, 


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Fig.  28.    Discharges  and  Velocities  of  Circular  Brick  and  Concrete  Sewers  Flowing  Full 
By  Kutter's  Formula  (rc=0.015). 

it  can  be  determined  by  noting  where  the  point  (found  in  2,  above)  of  inter- 
section of  the  given  grade  and  diameter  lines  falls  with  reference  to  the  inclined 
lines  marked  with  the  different  velocities,  estimating  by  the  eye  the  decimals 
of  a  foot  per  second. 

(B)  When  the  grade  and  the  required  discharge  are  given,  to  find  the  neces- 
sary diameter  of  pipe,  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  given  grade  is  found, 
interpolating  by  the  eye,  if  necessary,  between  the  grades  marked  on  the 
diagram.  (2)  Find  the  intersection  of  the  vertical  line  through  this  grade 
with  the  horizontal  line  through  the  given  discharge,  finding  the  discharge  on 
the  left  of  the  diagram  if  it  is  given  in  cubic  feet  per  second,  or  on  the  right  if 
it  is  given  in  gallons  per  24  hours.  (3)  Note  between  which  two  diameter 
lines  this  point  of  intersection  falls,  and  take  the  diameter  line  nearest  as  that 
required.  (4)  Also  note  the  position  of  the  point  of  intersection  with  refer- 
ence to  the  velocity  lines,  and  so  estimate  the  velocity,  interpolating  by  the  eye 
between  the  inclined  velocity  lines. 

(C)  When  the  velocity  and   diameter  are  given,  to  find  the  grade  and  dis- 
charge. 

(1)  Find  the  intersection  of  the  given  diameter  line  with  the  given 
velocity  line,  interpolating  by  the  eye,  if  necessary.  (2)  Then  vertically 


SEWERS  AND  DRAINS  49 

downward  to  the  bottom  of  the  diagram  from  this  point  of  intersection,  read 
the  required  grade;  and  horizontally  to  the  left  side  or  to  the  right  side  of  the 
diagram,  read  the  discharge,  interpolating  by  the  eye  in  each  case,  if  necessary. 
All  other  cases  may  be  solved  by  similar  obvious  methods. 


EXAMPLES 

Example  7.  What  size  of  circular  brick  or  concrete  sewer  laid  to 
a  0.2  per  cent  grade  will  be  required  to  carry  a  storm  sewage  flow  of 
f  cu.  ft.  per  second  per  acre  from  one  square  mile  of  drainage  area,  and 
what  will  be  the  velocity? 

Solution.  See  B,  above.  1  square  mile  =  640  acres.  The  capacity 
required  is  640  X  I  -  480  cu.  ft.  per  second,  which  we  find  on  the  left 
of  Fig.  28  just  below  the  500  cu.  ft.  per  second  horizontal  line,  interpolating 
by  eye.  We  next  find  the  0.2  per  cent  grade  line  at  the  bottom  of  the 
diagram,  and  locate  the  point  of  intersection  of  this  vertical  0 . 2  per  cent 
grade  line  with  the  horizontal  480  cu.  ft.  per  second  line  already  found 
above.  This  point  of  intersection  comes  nearly  on  the  9  feet  inclined 
diameter  line,  and  between  the  seven  and  eight  feet  per  second  inclined 
velocity  lines. 

Answer.  Diameter  of  sewer  required,  9  feet.  Velocity  =  7.6  ft.  per 
second. 

Example  8.  What  will  be  the  minimum  grade  for  a  60-inch  brick 
or  concrete  sewer,  if  the  minimum  velocity  allowed  when  flowing  full  is 
3  ft.  per  second? 

Answer.     See  C,  above.     0.067  per  cent  grade. 

Example  9.  How  large  a  population,  contributing  75  gallons  per 
capita  per  day  of  sanitary  sewage,  on  the  average  (the  maximum  flow 
being  3  times  the  average),  can  be  served  by  a  48-inch  circular  brick 
sewer,  laid  to  a  0.06  per  cent  grade;  and  what  will  be  the  velocity  of 
flow?  (NOTE:  Find  the  capacity  as  in  A,  above;  and  then  divide  by 
3  times  the  average  per  capita  amount  per  day.) 

Answer.     89,000   population.     2.4   ft.   per  second. 

Example  10.  What  will  be  the  grade  required  to  force  a  flow  of 
500  cu.  ft.  per  second  through  a  96-inch  circular  brick  sewer? 

Answer.     0.38  per  cent  grade. 

42.  Diagram  of  Discharges  and  Velocities  of  Egg=Shaped 
Brick  and  Concrete  Sewers  Flowing  Full.  Fig.  29  is  the  diagram  for 
egg-shaped  brick  sewers,  corresponding  to  Fig.  27  for  circular  pipe 
sewers,  ana  to  Fig.  28  for  circular  brick  and  concrete  sewers. 


50 


SEWERS  AND  DRAINS 


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Fig.  29.    Discharges  and  Velocities  of  Egg-Shaped  Brick  and  Concrete  Sewers  Flowing 
Full.     By  Kutter's  Formula  (w=0.015). 

TO  USE  THE  DIAGRAM 

(A)  When  the  diameter  of  the  pipe  and  the  grade  are  given,  to  find  the 
discharge  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  grade  is  found, 
interpolating  by  the  eye,  if  necessary,  between  the  grades  marked  on  the 
diagram.  (2)  Find  the  point  where  the  vertical  line  through  the  given  grade 
intersects  the  inclined  line  marked  with  the  given  diameter  of  sewer.  (3) 
Trace  horizontally  through  this  point,  interpolating  by  the  eye,  if  necessary, 
between  the  horizontal  lines  on  the  diagram ;  and  r^ad  the  discharge  of  the  pipe 
running  full,  on  the  left  side  of  the  diagram  in  cubic  feet  per  second,  or  on  the 
right  side  of  the  diagram  in  gallons  per  24  hours.  (4)  If  the  velocity  is 
desired,  it  can  be  determined  by  noting  where  the  point  (found  in  2,  above) 
of  intersection  of  the  given  grade  and  diameter  lines  falls  with  reference  to  the 
inclined  lines  marked  with  the  different  velocities,  estimating  by  the  eye  the 
decimals  of  a  foot  per  second. 

(J5)  When  the  grade  and  the  required  discharge  are  given,  to  find  the 
necessary  diameter  of  pipe,  and  the  velocity. 

(1)  Look  along  the  bottom  horizontal  line  till  the  given  grade  is  found, 
interpolating  by  the  eye,  if  necessary,  between  the  grades  marked  on  the  dia- 
gram. (2)  Find  the  intersection  of  the  vertical  line  through  this  grade  with 
the  horizontal  line  through  the  given  discharge,  finding  the  discharge  on  the 
left  of  the  diagram  if  it  is  given  in  cubic  feet  per  second,  or  on  the  right  if  it 
is  given  in  gallons  per  24  hours.  (3)  Note  between  which  two  diameter  lines 
this  point  of  intersection  falls,  and  take  the  diameter  line  nearest  as  that 
required.  (4)  Also  note  the  position  of  the  point  of  intersection  with  refer- 
ence to  the  velocity  lines,  and  so  estimate  the  velocity,  interpolating  by  the 
eye  between  the  inclined  velocity  lines. 


SEWERS  AND  DRAINS  51 

(C)  When  the  velocity  and  diameter  are  given,  to  find  the  grade  and  dis- 
charge. 

(1)  Find  the  intersection  of  the  given  diameter  line  with  the  given 
velocity  line,  interpolating  by  the  eye,  if  necessary.  (2-)  Then  vertically 
downward  to  the  bottom  of  the  diagram  from  this  point  of  intersection,  read 
the  required  grade;  and  horizontally  to  the  left  side  or  to  the  right  side  of  the 
diagram,  read  the  discharge,  interpolating  by  the  eye  in  each  case,  if  necessary. 

All  other  cases  may  be  solved  by  similar  obvious  methods. 

EXAMPLES 

Example  11.  What  will  be  the  discharge  and  velocity  of  flow  of 
a  4  by  6-feet  egg-shaped  brick  or  concrete  sewer  flowing  full  and  laid 
to  a  0.4  per  cent  grade? 

Solution.  See  A,  above.  Find  the  0.4  per  cent  grade  line  at  the 
bottom  of  Fig.  29,  and  locate  the  point  of  intersection  of  the  vertical 
line  through  this  point  with  the  inclined  4  by  6  dimension  line.  Then 
tracing  horizontally  to  the  left,  we  estimate  by  the  eye  128  cu.  ft.  per 
second  for  the  discharge.  We  also  note  that  the  point  of  intersection 
of  the  vertical  0.4  per  cent  grade  line  with  the  inclined  4  by  6  dimension 
line  found  above,  is  practically  on  the  inclined  7  ft.  per  second  velocity 
line. 

Answer.  Discharge,  128  cu.  ft.  per  second.  Velocity,  7  ft.  per 
second. 

Example  12.  What  will  be  the  size  of  egg-shaped  brick  or  con- 
crete sewer  required  to  carry  a  storm  flow  of  J  cu.  ft.  per  second  per  acre 
from  a  drainage  area  of  \  square  mile  (=320  acres),  the  grade  being 
0.3  percent? 

Answer.     See  B,  above.     4  ft.  6  in.  by  6  ft.  9  in. 

Example  13.  A  6-foot  circular  sewer  and  a  5  by  7  ft.  6-in.  egg- 
shaped  sewer  have  nearly  the  same  area  of  cross-section.  If  both  are 
laid  to  a  0 . 2  per  cent  grade,  find  the  discharge  and  velocity  of  each  when 
flowing  full.  (NoTE:  Solve  by  Figs.  28  and  29.  See  A,  above.) 

Answer.  Discharge,  165  cu.  ft.  per  second;  and  velocity,  5.8  ft. 
per  second,  for  the  circular  sewer;  and  discharge  163  cu.  ft.  per  second; 
and  velocity,  5.7  ft.  per  second,  for  the  egg-shaped  sewer. 

NOTE:  Although  the  egg-shaped  sewer  has  a  slightly  smaller 
velocity  when  both  are  flowing  full,  it  has  a  materially  greater  velocity 
than  the  circular  sewer  for  small  depths  of  flow. 

Example  14.  If  the  minimum  allowable  velocity  of  flow  in  storm 
sewers  is  3  ft.  per  second,  find  the  minimum  allowable  grades  for  2  ft.  by 
3  ft.,  4  ft.  by  6  ft.,  and  6  ft.  by  9  ft.  egg-shaped  sewers,  respectively. 

Answer.     See  C,  above.     0 . 20,  0 . 08,  and  0 . 05  per  cent,  respectively. 


52 


SEWERS  AND  DRAINS 


43.  Diagram  of  Discharges  and  Velocities  in  Circular  Sewers 
at  Different  Depths  of  Flow.  The  diagrams  so  far  given  show  the 
discharges  and  velocities  in  sewers  flowing  full.  It  often,  however, 
is  necessary  to  be  able  to  calculate  the  discharge  and  the  velocity 
when  the  sewer  flows  only  partially  full. 

For  circular  sewers,  the  discharges  and  velocities,  when  flowing 
only  partially  full,  can  readily  be  determined  by  the  use  of  the  dia- 
gram, Fig.  30,  in  connection  with  Figs.  27  and  28. 


O       Ql       Q2      O.3      O.4     0.5      O.6     O7     O.6     O.9       I.O      I.I        l£ 

Proportional  Velocities  and  Discharges. 

Fig.  30.    Diagram  Showing  Changes  in  Velocity  and  Discharge  in  Circular  Sewers  for 
Different  Depths  of  Flow. 


TO  USE  THE  DIAGRAM 

(A)  When  the  depth  of  flow  is  given,  together  with  the  diameter  and  grade 
of  the  sewer,  to  determine  the  discharge  and  the  velocity. 

(1)  By  Fig.  27  if  a  pipe  sewer,  or  by  Fig.  28  if  a  brick  or  concrete  sewer, 
determine  the  discharge  and  velocity  of  the  sewer  flowing  full.  (2)  Divide 
the  given  depth  of  flow  by  the  given  diameter,  to  determine  the  proportional 
depth  of  flow;  and  find  this  proportional  depth  on  the  vertical  scale  towards  the 
left  of  Fig.  30,  interpolating  by  the  eye,  if  necessary.  (3)  Find  the  inter- 
section of  the  horizontal  line  through  the  proportional  depth  (found  in  2, 
above),  first,  with  the  proportional  discharge  line,  and,  second,  with  the  pro- 
portional velocity  line,  in  Fig.  30;  and  read  off  at  the  bottom  of  the  diagram 
vertically  below  these  intersection  points,  the  proportional  discharge  and  the 
proportional  velocity.  (4)  Multiply  the  discharge  and  velocity  flowing  full 
(found  in  1,  above),  by  the  proportional  discharge  and  proportional  velocity 


SEWERS  AND  DRAINS  53 

found  in  3,  above),  and  the  products  will  be  the  required  actual  discharge  and 
actual  velocity,  for  the  given  depth  of  flow. 

(B)  When  the  actual  discharge  is  given,  together  with  the  diameter  and 
grade  of  the  sewer,  to  find  the  depth  and  velocity  of  flow. 

(1)  By  Fig.  27  if  a  pipe  sewer,  or  by  Fig.  28  if  a  brick  or  concrete  sewer, 
determine  the  discharge  of  the  sewer  flowing  full.  (2)  Divide  the  given  dis- 
charge by  the  discharge  flowing  full,  to  determine  the  proportional  discharge; 
and  find  this  along  the  bottom  of  the  diagram  in  Fig.  30,  interpolating  by  the 
eye,  if  necessary.  (3)  Find  the  intersection  of  the  vertical  line  through  the 
proportional  discharge  (found,  in  2,  above)  with  the  proportional  discharge 
curve  in  Fig.  30;  and  horizontally  to  the  left,  read  off  on  the  vertical  scale  near 
jthe  left  of  the  diagram  the  proportional  depth  of  flow.  (4)  Multiply  the 
diameter  of  the  sewer  by  the  proportional  depth,  and  the  product  will  be  the 
actual  depth  of  flow  for  the  given  discharge.  (5)  The  actual  velocity  can  now 
be  found  as  described  above  for  case  A. 

All  other  cases  than  A  and  B  can  be  readily  solved  by  similar  obvious 
methods. 

EXAMPLES 

Example  15.  What  will  be  the  actual  discharge  and  velocity  of 
flow  in  a  48-inch  circular  brick  sewer  laid  to  a  0.  15  per  cent,  grade,  and 
flowing  6  inches  deep? 

Solution.  See  A,  above.  (1)  By  Fig.  28,  with  the  sewer  flowing 
full,  the  discharge  would  be  30,000,000  gallons  per  day,  and  the  velocity 


3  .  8  ft.  per  second  .    (2)       -  =0.12+=  proportional    depth    of 

48  inches 

flow,  which  we  find  on  the  vertical  scale  near  the  left  of  Fig.  30.  (3) 
Horizontally  opposite  the  point  found  in  2,  we  locate  points  on  the 
proportional  discharge  curve  and  the  proportional  velocity  curve  in  Fig. 
30;  and  vertically  beneath  these  points  we  read  at  the  bottom  of  the 
diagram,  0.04  =  proportional  discharge,  and  0.40  =  proportional 
velocity.  (4)  0.04  X  30,000,000  gallons  =  1,200,000  gallons  per  day 
=  actual  discharge  for  6  inches  depth  of  flow;  and  0.40  X  3.8  =  1.5 
ft.  per  second  =  actual  velocity  for  6  inches  depth  of  flow. 

Example  16.  An  8-inch  pipe  sewer,  laid  to  a  0.40  per  cent  grade, 
is  to  carry  the  sewage  of  500  people  contributing  100  gallons  each  per 
day.  What  will  be  the  average  depth  and  velocity  of  flow? 

Solution.  See  B,  above.  (1)  By  Fig.  27,  the  discharge  and 
velocity  flowing  full  would  be  respectively  450,000  gals,  per  day,  and  1.9 
ft.  per  second.  (2)  The  actual  discharge  is  500  X  100  =  50,000  gals. 

per  day,  and  hence  the  proportional  discharge  is  —  -    -  =0.11.     We  find 

4oU,uuu 

this  proportional  discharge  along  the  bottom  line  of  Fig.  30,  inter- 
polating by  eye.  (3)  Vertically  above  the  0.11  proportional  velocity, 


54 


SEWERS  AND  DRAINS 


we  find  a  point  on  the  proportional  discharge  curve ;  and  tracing 
horizontally  to  the  left,  we  there  read  off  the  proportional  depth  =  0.225. 
(4)  0.225  X  8  =  1 .8  inches  =  the  actual  depth  of  flow  for  the  given 
discharge.  (5)  Horizontally  to  the  right  from  the  0.225  proportional 
depth,  we  find  a  point  on  the  proportional  velocity  line;  and  vertically 
beneath  this  point  we  read  off  at  the  bottom  of  the  diagram,  proportional 
velocity  =  0.60.  Then  0.60  X  1.9  (see  1,  above)  =  1 . 1  ft.  per  second 
=  actual  velocity  for  the  given  depth. 

Example  17.  What  will  be  the  discharge  and  velocity  of  a  12-inch 
pipe  sewer  laid  to  a  0 . 25  per  cent  'grade  when  flowing  4  inches  deep  ? 

See  A,  above. 

Answer.  Discharge,  250,000  gals,  per  day;  velocity,  1.7  ft.  per  second. 

Example  18.     What  will  be  the  depth  and  velocity  of  flow  in  a 

"h 


Fig.  31. 


0      O.I     O.2    O.3   OA-    0.5   O.6     O.7    O.8    O.9     1.0     1.1      1.2 

Proportional  Velocities  and  Discharges 

Diagram  Showing  Changes  in  Velocity  and  Discharge  in  Egg-Shaped  Sewers  for 
Different  Depths  of  Flow. 


15-inch  pipe  sewer,  laid  at  a  0.2  per  cent  grade,  carrying  1,000,000 
gallons  of  sewage  per  day? 

See  B,  above. 

Answer.     Depth,  8  inches;  velocity,  2.3  ft.  per  second. 

44.  Diagram  of  Discharges  and  Velocities  in  Egg=Shaped 
Sewers  at  Different  Depths  of  Flow.  For  egg-shaped  sewers,  the 
discharges  and  velocities,  when  flowing  partially  full,  can  readily  be 
determined  by  the  diagram,  Fig.  31,  used  in  connection  with  Fig.  29. 


SEWERS  AND  DRAINS  55 

TO  USE  THE  DIAGRAM 

(A)  When  the  depth  of  flow  is  given,  together  with  the  diameter  and  grade 
of  the  sewer,  to  determine  the  discharge  and  the  velocity. 

(1)  By  Fig.  29,  determine  the  discharge  and  velocity  of  the  sewer  flow- 
ing full.  (2)  Divide  the  given  depth  of  flow  by  the  given  height  to  determine 
the  proportional  depth  of  flow,  and  find  this  proportional  depth  on  the  vertical 
scale  towards  the  left  of  Fig.  31,  interpolating  by  the  eye,  if  necessary.  (3) 
Find  the  intersection  of  the  horizontal  line  through  the  proportional  depth 
(found  in  2,  above),  first,  with  the  proportional  discharge  line,  and,  second, 
with  the  proportional  velocity  line,  in  Fig.  31 ;  and  read  off  at  the  bottom  of  the 
diagram,  vertically  below  these  intersection  points,  the  proportional  discharge, 
and  the  proportional  velocity.  (4)  Multiply  the  discharge  and  velocity  flowing 
full  (found  in  1,  above),  by  the  proportional  discharge  and  proportional  velocity 
(found  in  3,  above),  and  the  products  will  be  the  required  actual  discharge  and 
actual  velocity  for  the  given  depth  of  flow. 

(B)  When  the  actual    discharge  is  given,  together  with  the  diameter  and 
grade  of  the  sewer,  to  find  the  depth  and  velocity  of  flow. 

(1)  By  Fig.  29,  determine  the  discharge  of  the  sewer  flowing  full.  (2) 
Divide  the  given  discharge  by  the  discharge  flowing  full,  to  determine  the 
proportional  discharge,  and  find  this  along  the  bottom  of  the  diagram  in  Fig.  31, 
interpolating  by  the  eye,  if  necessary.  (3)  Find  the  intersection  of  the  vertical 
line  through  the  proportional  discharge  (found  in  2,  above),  with  the  propor- 
tional discharge  curve  in  Fig.  31,  and  horizontally  to  the  left,  read  off  on  the 
vertical  scale  near  the  left  of  the  diagram  the  proportional  depth  of  flow.  (4) 
Multiply  the  height  of  the  sewer  by  the  proportional  depth,  and  the  product 
will  be  the  actual  depth  of  flow  for  the  given  discharge.  (5)  The  actual  velocity 
can  now  be  found  as  described  above  for  case  A . 

All  other  cases  than  A  and  B  can  be  readily  solved  by  similar  obvious 

methods. 

EXAMPLES 

Example  19.  What  will  be  the  discharge  and  velocity  in  an  egg- 
shaped  brick  or  concrete  sewer  3  ft.  by  4  ft.  6  in.,  laid  to  a  0. 15  per  cent 
grade,  and  flowing  12  inches  deep? 

See  A,  above. 

Solution.  (1)  By  Fig.  29,  discharge  and  velocity  flowing  full  =  36 
cu.  ft.  per  second,  and  3 . 45  ft.  per  second,  respectively.  (2)  The  pro- 

12 

portional  depth  =  —  =  0 . 22,  which  we  find  at  left  of  Fig.  31.    (3)    We 
o4 

locate  the  intersections  of  the  horizontal  line  through  the  0 . 22  proportional 
depth  with  the  proportional  discharge  and  proportional  velocity  curves, 
respectively;  and  vertically  below  these  points  we  read  off,  at  the  bottom 
of  the  diagram,  proportional  discharge  =  0 . 08,  and  proportional  velocity 
=  0.63.  (4)  36  X  0.08  =  2.9  cu.  ft.  per  second  =  actual  discharge; 
3 . 45  X  0 . 63  =  2 . 2  ft.  per  second  =  actual  velocity. 

Answer.  Discharge  =  2.9  cu.  ft.  per  second;  velocity  =  2.2  ft 
per  second, 


56  SEWERS  AND  DRAINS 

Example  20.  What  will  be  the  depth  and  velocity  of  flow  in  an 
egg-shaped  brick  or  concrete  sewer  5  ft.  by  7  ft.  6  in.  dimensions,  laid  to 
a  0.10  per  cent  grade,  and  carrying  30  cu.  ft.  per  second  flow  of  sewage? 

See  B,  above. 

Solution.  (1)  By  Fig.  29,  the  discharge  and  velocity  flowing  full 
=  117  cu.  ft.  per  second  and  4.05ft.  per  second,  respectively.  (2)  Pro- 

30 
portional  discharge  =  =  0.26—,  which  find  at  bottom  of  Fig.  31. 

(3)  Vertically  above  the  0.26  proportional  discharge,  we  locate  a  point 
on  the  proportional  discharge  curve  in  Fig.  31,  and  horizontally  to  the 
left  from  this  point  read  off  the  proportional  depth  =  0.39.  (4) 
90  X  0,39  =  35  inches  =  actual  depth  of  flow.  (5)  Horizontally  to 
the  right  along  the  0 . 39  proportional  depth  line,  we  locate  a  point  on 
the  proportional  velocity  line;  and  vertically  beneath  this,  we  read  off, 
at  the  bottom  of  the  diagram,  proportional  velocity  =  0.845.  Then 
4 . 05  X  0 . 845  =  3 . 4  f t.  per  second  =  actual  velocity. 

Answer.     Depth  of  flow  =  35  inches;  velocity  =  3.4  ft.  per  second. 

Example  21.  What  will  be  the  discharge  and  velocity  in  an  egg- 
shaped  brick  or  concrete  sewer  2  ft.  by  3  ft.  dimensions,  laid  to  a  0 . 50 
per  cent  grade,  flowing  18  inches  deep  ? 

See  A,  above. 

Answer.  Discharge  =  5,900,000  gals,  per  day;  velocity  =  4.5  ft. 
per  second. 

Example  22.  What  will  be  the  depth  and  velocity  of  flow  in  an 
egg-shaped  brick  or  concrete  sewer  3  ft.  6  in.  by  5  ft.  3  in.  dimensions, 
laid  to  a  0 . 08  per  cent  grade,  carrying  25  cu.  ft.  per  second  of  sewage  ? 

See  B,  above. 

Answer.  Depth  of  flow  =  39  inches;  velocity  of  flow  =  2.9  ft. 
per  second. 

GENERAL  EXAMPLES  FOR  PRACTICE  WITH  FIGS.  27=31 

45.  The  solution  of  the  following  general  examples  will  further 
familiarize  the  student  with  the  principles  thus  far  explained. 

Example  23.  A  24-inch  sewer  is  to  be  laid  to  a  0 . 25  per  cent  grade, 
and  may  be  made  of  vitrified  sewer  pipe  or  of  brick.  Compare  the  dis- 
charges and  velocities  obtained  with  the  two  materials.  (NOTE:  Use 
Figs.  27  and  28.) 

Answer.    With  sewer  pipe,  discharge  =   7,200,000  gals,  per  day; 

velocity  =  3 . 6  ft.  per  second. 

With  brick,  discharge  =  6,000,000  gals,  per  day;  velocity 
=  3  ft.  per  second. 


SEWERS  AND  DRAINS  57 

Example  24.  A  combined  sewer,  laid  to  a  0.15  per  cent  grade, 
drains  an  area  requiring  either  a  3-foot  circular  or  a  2  ft.  6  in.  by  3  ft.  9  in. 
egg-shaped  brick  sewer.  (These  sizes  have  the  same  cross-sectional 
area,  and  nearly  the  same  discharges  and  velocities,  when  flowing  full.) 
The  dry-weather  flow  of  sewage  will  be  only  1,000,000  gallons  per  day. 
Calculate  the  dry-weather  depth  and  velocity  of  flow  with  each  design. 
(NOTE:  Use  Figs.  28  and  30,  and  Figs.  29  and  31.) 

Answer.     With  circular  sewer,  depth  =6.1  inches;  velocity  =1.6 

ft.  per  second. 

With  egg-shaped  sewer,  depth  =  9.2  inches;  velocity  = 
1.9  ft.  per  second. 

Example  25.  In  a  10-inch  pipe  sewer,  laid  to  a  one  per  cent  grade, 
the  maximum  depth  of  flow  observed  was  7  inches;  and  the  minimum, 
2  inches.  What  were  the  corresponding  discharges  ?  (NOTE:  Use  Figs. 
27  and  30.) 

Answer.     Maximum  discharge  =    1,100,000  gals,  per  day; 
Minimum  120,000     "       "      " 

Example  26.  What  size  of  circular  sewer  laid  to  a  0.08  per  cent 
grade  will  be  required  to  carry  the  sanitary  sewage  of  a  city  of  100,000 
population,  with  an  average  flow  of  sewage  of  150  gallons  per  capita  per 
day,  the  maximum  rate  of  flow  being  three  times  the  average? 

Answer.     5  ft.  3  in.  diameter. 

Example  27.  What  size  of  egg-shaped  combined  sewer,  laid  to  a 
0 . 07  per  cent  grade  will  be  required  to  carry  a  storm  sewage  flow  of  0 . 5 
cu.  ft.  per  second  per  acre  from  a  drainage  area  of  320  acres  ? 

Answer.     6  ft.  by  9  ft. 

46.  Summary  of  Laws  of  Flow  in  Sewers.  The  principles 
discussed  in  Articles  38  to  44,  inclusive,  may  be  briefly  summarized 
as  follows: 

•  (1)     The  laws  of  flow  for  sewage    are  the  same  as  for  water. 

(2)  Kutter's  formula  is  .generally    considered  most  reliable  for 
calculating  the  flow  in  sewers,  though  complicated  to  use  directly. 

(3)  In  Kutter's  formula,  the  values  of  the  coefficient  of  rough- 
ness generally  used  for  sewer  computations,  are  n  =  0.013  for  pipe 
sewers,  and  n  =  0.015  for  brick  and  concrete  sewers. 

(4)  Sewer  diagrams  greatly  simplify   sewer  computations,  and 
are  presented  in  Figs.  27  to  31,  inclusive,  for  circular  and  egg-shaped 
sewers,  with  full  instructions  for  use. 

(5)  In  Fig.  30,  the  laws  of  flow  for  different  depths  of  flow  in 


58  SEWERS  AND  DRAINS 

circular  sewers  are  shown.     An  examination  of  the  diagram  brings 
out  this  important  law: 

In  circular  sewers  flowing  half-full,  the  velocity  is  the  same  as 
when  the  sewer  flows  full;  and  hence  the  discharge  flowing  half -full  is 
just  half  the  discharge  flowing  full. 

(6)  Figs.  30  and  31  also  show    the  following  important  law  of 
flow: 

In  a  sewer  of  any  shape,  not  flowing  under  pressure,  the  maximum 
discharge  and  velocity  will  occur,  not  with  the  sewer  flowing  full,  but 
with  it  flowing  a  little  less  than  full. 

This  is  due  to  the  increased  friction  against  the  top  of  the  sewer 
when  it  flows  full.  Owing  to  this  law,  no  sewer  can  flow  full  without 
being  under  pressure. 

(7)  In  the  case  of  combined  sewers   having  a  dry-weather  flow 
very  small  as  compared  with  the  storm  flow,  egg-shaped  sewers  give 
materially  greater  depths  and  velocities  of  dry-weather  flow  than 
circular  sewers. 

CALCULATIONS  OF  SIZES  AND  MINIMUM  GRADES  OF 
SEPARATE  SANITARY  SEWERS 

47.  Minimum  Sizes  of  Sanitary  Sewers.  In  the  early  con- 
struction of  sewers,  previous  to  the  last  half  of  the  19th  century,  the 
laterals  and  sub-mains  were  usually  made  very  much  larger  than  the 
amount  of  sewage  would  require,  with  the  idea,  apparently,  that  the 
bigger  the  sewer  the  better.  Such  badly  proportioned  sewers  were 
in  great  danger  of  stoppages  from  the  inability  of  the  shallow,  trick- 
ling stream  to  carry  along  the  solid  matter.  In  fact,  the  sewers  were 
expected  to  form  deposits,  and  were  purposely  made  large  to  hold 
a  large  amount  of  deposit  and  to  enable  men  to  enter  for  the  purpose 
of  cleaning  them.  Disastrous  sanitary  experience  with  such  foul 
sewers  made  it  apparent  that  there  was  just  as  much  danger  from 
making  the  sewers  too  large  as  from  making  them  too  small,  especially 
in  the  case  of  sanitary  sewers.  Such  sewers  should  be  made  small 
enough  to  give  a  good  depth  and  velocity  of  flow. 

Sanitary  sewers  should  not  be  made  small  enough,  however,  to 
cause  frequent  stoppages  by  catching  articles  which  have  been 
admitted  into  them  through  the  house  connections.  House  owners  are 
often  reprehensibly  negligent  in  putting  into  their  plumbing  fixtures, 


SEWERS  AND  DRAINS 


59 


articles  which  should  be  carefully  excluded.  On  this  account,  the 
size  of  house  connections  should  be  restricted  to  4  inches. 

An  8-inch  sewer  pipe  will  practically  always  carry  freely,  even 
crosswise,  any  article  which  can  come  lengthwise  around  the  traps 
and  bends  in  4-inch  soil-pipes  and  house  connections  Hence  eight 
inches  should  usually  be  adopted  as  the  minimum  size  for  sanitary 
sewers. 

Usually  the  great  bulk  of  the  sanitary  sewers  in  a  separate  system 
will  be  of  this  minimum  size,  only  a  limited  length  of  the  larger  sizes 
being  required  for  sub-mains  and  mains.  See  the  sewerage  map  of 
Ames,  Iowa,  Fig.  38. 

In  the  early  use  of  the  separate  system,  many  6-inch  laterals 
were  constructed,  and,  except  for  occasional  stoppages  from  articles 
improperly  put  into  the  sewers,  they  have  worked  well.  Som/*  engi- 
neers still  use  six  inches  as  the  minimum  size. 

48.  Minimum  Grades  and  Velocities  for  Separate  Sanitary 
Sewers.  In  the  design  and  construction  of  sewers  it  has  been  found 
that  certain  minimum  grades  should  be  adopted  to  prevent  deposits, 
no  sewers  being  built  to  lighter  grades  than  the  minimum  unless 
special  means  for  flushing,  or  special  facilities  for  cleaning,  are  pro- 
vided. This  is  to  insure  sufficient  velocity  to  prevent  the  settling-out 
of  the  solid  matter  in  the  sewage  to  form  deposits  in  the  sewers. 

These  minimum  grades  for  separate  sanitary  sewers  are  as 
follows : 

TABLE  II 
Minimum  Grades  for  Separate  Sanitary  Pipe  Sewers 


DIAMETER 

MINIMUM  GRADE 

DIAMETER 

MINIMUM  GRA.^E 

4  inches 

1  .  20  per  cent 

18  inches 

0.12  percent 

6 

0.67 

20 

0.10 

8 

0.43 

24 

0.08 

9 

0.36 

.     i 

27 

0.07 

10 

0.30 

30 

0.06 

12 

0.23 

33 

0.05 

15 

0.16 

36 

0.045 

CAUTION. — For  the  above  minimum  grades  to  be  satisfactory  and  safe,  then 
must  be  enough  sewage  to  give  a  good  depth  of  flow. 

The  flow  and  velocity  in  a  sewer  fluctuate  greatly,  as  illustrated 
in  Article  52,  below,  the  velocity  at  low  flow  being  much  less  than  when 
flowing  full  or  half-full. 


60  SEWERS  AND  DRAINS 

Experiments  have  shown  that  an  actual  velocity  of  1J  to  1J  feet 
per  second  is  sufficient  to  prevent  deposits  of  the  solid  matters  usually 
found  in  sanitary  sewers;  but  to  secure  this  velocity  at  low  flow 
requires  about  2  feet  per  second  when  the  sewer  flows  full  or  half-full 
(see  Figs.  30  and  31  for  the  fluctuation  of  velocity  with  depth  of  flow). 
Hence  the  minimum  grades  for  sanitary  sewers  should  usually  be 
those  giving  a  velocity  of  2  feet  per  second  when  flowing  full  or  half -full, 
as  shown  by  the  diagrams,  Figs.  27,  28,  and  29. 

It  is  usually  considered  that,  within  a  reasonable  period  in  the 
future,  the  increased  high-water  flow  each  day  should  be  sufficient  to 
fill  the  sewer  half-full  or  nearly  so.  However,  in  numerous  cases, 
sanitary  sewers  have  been  observed  to  work  well  at  the  above  grades 
with  less  depths  of  flow  than  this. 

Much  will  depend  on  the  nature  of  the  sewage.  Some  thick, 
manufacturing  sewages,  heavily  loaded  with  solid  matter,  would 
require  considerably  heavier  grades  to  insure  self-cleansing. 

Where  it  is  absolutely  impossible  to  secure  the  above  minimum 
grades,  special  means  for  flushing,  such  as  automatic  flush-tanks 
placed  about  three  blocks  apart,  should  be  used. 

49.  General  Explanation  of  the  Calculation  of  Amount  of 
Sanitary  Sewage.  The  first  thing  necessary  in  computing  the  size 
required  for  any  particular  sanitary  sewer,  is  to  ascertain  the  amount 
of  sewage  it  must  carry.  While  this  cannot  be  foretold  with  exact- 
ness, yet,  by  well-established  methods,  an  approximation  sufficiently 
close  for  all  practical  purposes  can  readily  bs  made. 

The  first  step  in  computing  the  amount  of  sewage  will  be  to 
estimate  the  future  tributary  population  which  may  use  the  sewer. 
For  this,  see  Art.  50,  below. 

The  second  step  will  be  to  estimate  the  average  amount  of  sewage 
contributed  by  each  person  per  day — that  is,  the  average  flow  of  sewage 
per  capita  per  day.  This,  multiplied  by  the  tributary  population,  will 
give  the  total  average  amount  of  sewage  per  day  which  the  sewer 
must  carry. 

Two  methods  are  in  use  for  estimating  the  average  flow  of  sewage 
per  capita  per  day: 

(1)  It  is  often  assumed  to  equal  the  average  consumption  cr 
water  per  capita  per  day.     For  this  method,  see  Art.  51,  below. 

(2)  The  best  method  is  to  compare  the  local  conditions  with 


SEWERS  AND  DRAINS  61 

actual  sewer  gaugings  of  flow  in  sewers  under  similar  conditions 
elsewhere.  For  this  method,  see  Art.  52,  below. 

50.  Methods  of  Estimating  the  Population  Tributary  to  Sanitary 
Sewers.  The  most  important  difficulty  encountered  in  estimating  the 
population  tributary  to  sanitary  sewers,  is  the  fact  that  it  is  the  future 
population  which  must  be  determined.  To  know  the  present  tribu- 
tary population  is  not  sufficient.  Two  methods  will  be  described: 

(1)  The  best  method  of  estimating  the  future  population  tributary 
io  sanitary  sewers  is  as  follows: 

(a)  On  the  sewer  map,  lay  out  sewers  to  serve  all  districts  to 
be  served  in  the  future  as  well  as  at  present. 

(b)  After  careful  examination  of  the  ground,  and  study  of  the 
conditions,  estimate  the  number  of  persons  tributary  to  the  sewers 
per  100  feet  of  sewers  in  each  district  when  it  is  built  up  as  fully  as  can 
reasonably  be  expected. 

In  doing  this,  five  or  six  persons  per  family  should  usually  be 
allowed,  and  the  number  of  families  on  both  sides  of  the  street  for  one 
block  in  the  future  estimated.  The  number  of  persons  per  block  so 
obtained  should  then  be  divided  by  the  number  of  hundred  feet  of 
sewer  per  block  from  center  to  center  of  streets. 

Thus,  if  there  are  6  lots  50  feet  wide  per  block  (=300  feet)  on 
each  side  of  the  sewer,  and  the  streets  are  60  feet  wide  (=360  feet 
center  to  center  of  streets),  and  if  it  is  thought  that  every  lot  will 
eventually  contain  one  residence, 

Tributary  population  =  -    — -  ^rSC     :  ==  20  persons  per  100  feet  of  sewer. 

The  tributary  population  per  100  feet  of  sewer  will  usually  range 
from  20  persons  in  the  residence  districts  of  small  cities,  to  100  persons 
in  thickly  built-up  business  districts.  In  the  congested  districts  of 
the  largest  cities,  the  population  is  still  denser. 

(c)  To  determine  the  total  population  tributary  above  any  point  on 
a  sanitary  sewer,  scale  from  the  sewer  map  the  total  number  of  hundred 
feet  of  tributary  sewer  above  that  point,  including  all  branches;  and 
multiply  the  total  so  obtained  by  the  tributary  population  per  100  feet 
of  sewer. 

Thus,  if  there  are  8,500  ft.  of  tributary  sewers,  and  the  tributary 
population  is  20  per  100  ft.,  the  total  tributary  population  will  =156  X 
20  =  3,120  persons.  In  some  cases  part  of  the  length  of  tributary 


62 


SEWERS  AND  DRAINS 


sewers  may  have  to  be  multiplied  by  one  density  of  tributary  population; 
and  part  by  another. 

(2)  In  case  the  future  population  of  an  entire  city  is  to  be 
estimated,  a  different  method  must  be  used. 

Usually,  the  past  population  of  the  city  at  different  dates  is 
obtained  from  census  reports;  and  by  study  of  this  past  growth,  and 
of  the  present  and  probable  future  local  conditions  as  affecting  growth, 
and  by  comparison  with  the  past  growth  of  larger  cities  whose  con- 
ditions were  similar,  estimates  are  made  of  the  probable  future  popu- 
lations at  different  dates,  for  20  to  50  years  in  the  future. 

Usually,  also,  the  past  records  of  the  city  that  is  being  studied, 
and  of  others,  are  platted  as  curves  on  cross-section  paper,  the  ordi- 
nates  representing  population,  and  the  abscissa?  dates;  and  the 
future  estimates  are  made  by  prolonging  the  curve  of  growth  into  the 
future. 

51.  Use  of  Statistics  of  Water  Consumption  in  Determining 
the  Per  Capita  Flow  of  Sanitary  Sewage.  Since  about  99.8  per  cent 
of  sanitary  sewage  is  merely  ordinary  water,  nearly  always  taken  from 
the  public  supply,  the  total  flow  per  capita  of  sanitary  sewage  is  usually 
approximately  equal  to  the  consumption  of  water  per  capita  (that  is. 


140 

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A.M. 


P.M. 


Fig.  32.    Typical  Gauging  of  Flow  of  Sanitary   Sewage,  Des   Moines,   Iowa,   Friday 

per  person).     In  Fig.  32  may  be  seen  how  closely  sewage  flow  and 
water  consumption  ordinarily  correspond. 


SEWERS  AND  DRAINS 


63 


In  many  towns,  however,  there  will  not  be  such  close  corre- 
spondence. Sometimes  considerable  amounts  of  water  may  be  used 
for  manufacturing  or  other  purposes  which  divert  it  from  the  sewers, 
making  the  sewage  flow  less  than  the  water  consumption.  More 
often  there  will  be  considerable  influxes  of  ground  water  through  leak- 
ing sewer  joints,  sometimes  making  the  sewage  flow  several  times  as 
great  as  the  water  consumption. 

However,  very  extensive  statistics  of  water  consumption  in 
a  large  number  of  places  have  been  collected,  while  actual  gaugings 
of  flow  of  sewage  are  comparatively  few.  Hence  statistics  of  the 
water  consumption  of  the  town  for  which  sewers  are  being  designed, 
or  of  similar  towns  elsewhere,  are  often  used  as  the  basis  for  estimating 
the  per  capita  flow  of  sanitary  sewage.  In  studying  each  town 

TABLE  III 
Consumption  of  Water  in  American  Cities,  1895 


CITY 

POPULATION 

DAILY  CONSUMPTION  PER 
PERSON,  1895.     GALLONS 

New  York 

3,  437,  202 

100 

Chicago 

1,698,575 

139 

Philadelphia 

1,293,697 

162 

St.  Louis 

575,  238 

98 

Boston 

560,  892 

100 

San  Francisco 

342,  782 

63 

Buffalo 

352,  387 

271 

New  Orleans 

287,  104 

35 

Minneapolis 
Columbus 

202,  718 
125,  560 

88 
127 

Atlanta 

89,  872 

42 

Nashville 

80,  865 

139 

preliminary  to  designing  sewers  for  it,  all  possible  information  should 
be  secured  relative  to  its  water  consumption. 

On  pages  4  to  10  of  the  instruction  paper  on  Water  Supply, 
Part  I,  will  be  found  a  detailed  discussion  of  water  consumption. 
From  a  larger  table  given  there,  Table  III  herewith  is  condensed,  to 
show  how  the  average  per  capita  water  consumption  varies  in  dif- 
ferent American  cities. 

It  will  be  noted  that  there  is  a  very  wide  range  in  water  con- 
sumption. The  excessively  low  rates  usually  mean  an  incomplete 
water  supply,  which  is  likely  to  be  extended  later,  while  the  excessively 
high  rates  usually  mean  great  waste  of  water.  This  can  often  be 
greatly  reduced  by  introducing  water  meters. 


64 


SEWERS  AND  DRAINS 


Under  fairly  average  conditions  the  consumption  will  usually 
fall  between  the  limits  of  40  and  125  gallons  per  capita  per  day,  as 
shown  in  detail  in  Table  IV. 

TABLE  IV 
Water  Consumption  under  Ordinary  Conditions 


USE 

GALLONS  PER  CAPITA  PER  DAY 

Minimum 

Average 

Maximum 

Domestic 
Commercial 
Public 
Waste  and  Loss 

15 
7 
3 
15 

25 
20 
5 
25 

40 
35 
10 
40 

Total 

40 

75 

125 

52.  Use  of  Sewer  Qaugings  in  Determining  the  Per  Capita 
Flow  of  Sanitary  Sewage.     It  has  already  been  stated  that  the  flow 
of  sanitary  sewage  is  not  always  equal  to  the  water  consumption.     In 
one  case  of  sewer  gaugings,  the  writer  found  the  flow  of  sewage  to  be 
only  50  to  60  per  cent  of  the  water  consumption,  the  remainder  of  the 
water  being  consumed  for  purposes  which  diverted  it  from  the  sewers. 
In  another  case  of  sewer  gaugings,  the  writer  found  the  flow  of  sewage 
to  be  over  500  per  cent  of  the  water  consumption,  the  increase  being 
due  to  infiltration  of  ground  water  through  sewage  joints.     Hence, 
water  consumption  data  alone  are  not  sufficient  in  making  estimates 
of  sewage  flow,  and  data  from  actual  sewer  gaugings  are  needed. 
Of  late  years  there  is  an  increasing  accumulation  of  data  of  sewage 
flow  obtained  from  actual  gaugings.     Some  of  these  data  are  given  in 
Table  V. 

At  the  Iowa  State  College,  the  sewage  flow,  as  given  in  Table  V, 
below,  was  50  to  60  per  cent  of  the  water  consumption,  owing  to  uses 
of  water  which  diverted  it  from  the  sewers.  At  Grinnell,  on  the  other 
hand,  infiltration  of  ground  water  into  the  sewers  increased  the  sewage 
flow  to  about  six  times  the  total  water  consumption  on  the  same  day. 

A  study  of  Table  V  will  show,  however,  that  in  general  the 
average  flow  of  sanitary  sewage  is  between  the  limits  of  50  and  125  gal- 
lons per  capita  per  day. 

53.  Capacities  of  Sanitary  Sewers  Required  to  Provide  for 
Fluctuations  in  the  Rate  of  Flow.     So  far  our  discussion  of  flow  of 


SEWERS  AND.  DRAINS 


65 


TABLE  V 
Gaugings  of  Flow  of  Sanitary  Sewage 


SEWER 

DATE 

DURA- 
TION, 
DAYS 

TRIBU- 
TARY POP- 
ULATION 

SEWAGE  FLOW,   GALS. 
PER  CAPITA  PER  DAY 

Min. 

Av. 

Max. 

Compton  Ave.,  St.  Louis 

1880 

6 

8,200 

65 

102 

149 

College  St.,  Burlington,  Vt. 

1880 

5-8 

325 

65 

115 

140 

Huron  St.,  Milwaukee,  Wis. 

1880 

3,174 

120 

Memphis,  Tenn. 

1881 

_ 

20,  000 

61 



140 

13  Sewers,  Providence,  R.  I. 

1884 

1-6 

33,  825 

— 

78 



Asylum,  Binghamton,  N.  Y. 

1888 

- 

1,300 

— 

— 

608 

16  Sewers,  Toronto,  Ont. 

1891 

3 

168,  081 

— 

87 



Insane  Asylum,  Weston,  W.  Va. 

1891 

2 

1,000 

40 

91 

151 

Schenectady,  N.  Y. 
Canton,  Ohio 

1892 
1893 

1 

*10,  000 
40,  000 

72 
54 

86 
129 

103 
180 

Chautauqua,  N.  Y. 

1894 

_ 

7,000 

6 

20 

30 

Iowa  State  College,  Ames,  la. 

1894 

7 

289 

0 

32 

77 

Des  Moines,  la.,  E.  Side 

1895 

15 

8,100 

22.5 

74 

142 

Des  Moines,  la.,  W.  Side 

1895 

13 

19,  400 

23.2 

66 

175.3 

Iowa  State  College,  Ames,  la. 

1900 

2 

800 

54 

95 

175 

Iowa  State  College,  Ames,  la. 

1900 

28 

800 

30 

57 

130 

Marshalltown,  la. 

1900 

1 

4,200 

67 

85 

111 

Grinnell,  la. 

1901 

1 

2,000 

169 

186 

200 

Insane  Asylum,  Mt.  Pleasant,  la. 

1901 

1 

1,200 

32 

62 

115 

Waverly,  N.  Y. 

1905 

4 

1,796 

79 

155 

194 

*  Estimated. 

sanitary  sewage  (Arts.  51  and  52)  has  referred  particularly  to  the 
average  flow  per  capita  per  day.  The  flow,  however,  is  not  uniform, 
but  fluctuates  greatly.  First,  there  is  a  seasonal  fluctuation.  The 
flow  is  apt  to  be  especially  high  in  severe  cold  weather,  when  faucets 
are  left  running  to  keep  pipes  from  freezing;  in  hot  weather,  when 
water  consumption  is  high;  and  in  wet  weather,  when  some  ground 
water  finds  its  way  into  the  sewers. 

Second,  there  is  a  daily  fluctuation.  For  example,  gaugings 
show  that  the  flow  usually  is  light  on  Sundays  and  holidays,  when 
business  is  suspended.  The  flow  on  Monday  is  apt  to  be  especially 
high,  on  account  of  wash  day. 

Third,  there  is  an  hourly  fluctuation,  at  different  times  of  the  day 
and  night.  In  Fig.  32,  an  example  is  shown  of  the  fluctuation  of 
sewage  flow  throughout  one  day,  as  determined  by  a  continuous 
sewer  gauging  in  the  case  of  a  city  of  56,000  population.  As  shown 
in  this  figure,  the  flow  of  sanitary  sewage  is  usually  low  through  the 
night,  reaching  a  minimum  at  'about  2  to  3  A.  M.  It  increases 
rapidly  early  in  the  morning,  reaching  a  high  point  at  about  10  to 
11  A.  M.  Although  there  is  usually  a  temporary  drop  at  the  noon 


66  SEWERS  AND  DRAINS 

hour,  the  flow  continues  high  until  early  evening,  and  then  decreases 
rapidly  to  its  low  night  value. 

A  study  of  the  sewer  gaugings  summarized  in  Table  IV,  together 
with  others,  shows  that  the  flow  of  sanitary  sewage  ordinarily  fluc- 
tuates from  a  minimum  rate  of  30  per  cent  to  a  maximum  rate  of  265 
per  cent  of  the  average  rate.  If  the  gaugings  had  been  extended  over 
longer  periods  of  time,  still  greater  fluctuations  of  flow  would  certainly 
have  been  found. 

It  is  apparent  that  the  fluctuations  in  rate  of  flow  will  be  greater 
in  lateral  sewers  than  in  main  sewers.  To  make  them  large  enough 
to  provide  for  the  greatest  rates  of  flow  to  be  reasonably  expected, 
sanitary  sewers  should  be  given  the  following  capacities: 

PROPER  CAPACITIES  OF  SANITARY  SEWERS 

For  lateral  sewers,  350  per  cent  of  the  average  flow. 
For  sub-main  sewers,  325  per  cent  of  the  average  flow. 
For  main  sewers,  300  per  cent  of  the  average  flow. 

Table  VI  (page  68)  is  proportioned  on  the  above  basis. 

54.  Ground  Water  in  Sanitary  Sewers.  In  addition  to  the 
sanitary  sewage  itself,  provision  must  often  be  made  in  separate  sani- 
tary sewers  for  leakage  of  ground  water  into  the  sewers.  The  amount 
of  ground  water  to  be  allowed  for,  will  depend  on  the  character  of  the 
soil,  on  the  height  of  the  ground  water  with  reference  to  the  sewer,  and 
on  the  care  with  which  the  sewer  joints  are  made.  //  the  joints  are 
made  very  carefully,  the  amount  of  ground  water  to  be  expected  may 
range,  with  the  soil,  and  height  of  ground  water,  from  0  to  30,000  gal- 
lons per  mile.  This  will  constitute,  say,  0  to  30  per  cent  of  the  sew- 
age, but  is  a  steady  flow,  not  requiring  the  300  to  350  per  cent  allow- 
ance for  fluctuations  required  for  sewage  (see  Art.  53).  Hence,  if  the 
joints  are  carefully  made,  the  capacity  of  the  sewers  need  not  be  in- 
creased more  than  10  per  cent  for  ground  water. 

If  sub-drains  with  outlets  separate  from  the  sewers  are  provided  for 
all  wet  stretches  of  trench,  no  allowance  whatever  for  ground  water  need 
be  made  in  the  size  of  the  sewers. 

The  infiltration  of  ground  water  is  apt  to  be  much  greater  during 
and  immediately  after  the  construction  of  sewers  than  later,  for  the 
effect  of  ,sewers  is  to  lower  permanently  the  level  of  the  ground 
water. 


SEWERS  AND  DRAINS  67 

55.  Summary  of  Methods  of  Computing  Sizes  of  Separate 
Sanitary  Sewers.  The  methods  for  computing  the  sizes  of  sanitary 
sewers  may  be  summarized  as  follows: 

(1)  Lay  out  on  the  sewer  map  all  the  sewers  required  to  serve 
all  districts  which  can  reasonably  be  expected  to  be  included  in  the 
system,  either  at  present  or  within  say  30  to  50  years  in  the  future. 

(2)  By  a  careful  study  of  the  topography,  business  conditions, 
manufacturing  possibilities,   and   other   future   prospects,    together 
with  the  sizes  of  blocks  and  lots,  and  the  widths  of  streets,  determine 
the  probable  future  tributary  population  in  each  district  per  100 
feet  of  sewer,  allowing  usually  five  or  six  persons  per  family. 

(3)  By  a  careful  study  of  the  statistics  of  water  consumption 
(Art.  51),  and  by  comparison  with  actual  sewer  gaugings  (Art.  52), 
taking  into  account  all  local  conditions,  estimate  the  average  flow  of 
sewage  in  gallons  per  capita  per  day. 

(4)  Beginning  at  the  upper  ends  of  the  sewers,  scale  from  the 
map  and  tabulate  the  total  lengths  of  tributary  sewer  above  suc- 
cessive points  in  the  system,  to  the  outlet.     Multiply  the  number  of 
hundreds  of  feet  in  these  lengths  by  the  tributary  population  per  100 
feet,  and  by  the  average  per  capita  flow  of  sewage  per  day,  to  get  the 
total  flow  of  sanitary  sewage  at  the  successive  points. 

(5)  To  allow  for  fluctuations  (Art.  53),  multiply  the  above 
average  rates  of  flow  of  sanitary  sewage  by 

3J  for  lateral  sewers; 
3J  "   sub-main    " 
3     "   main 
to  get  the  maximum  rates  of  flow  of  sanitary  sewage. 

(6)  To  the  maximum  rates  of  flow  so  found,  add  0  to  30,000 
gallons  per  mile  of  tributary  sewers,  to  allow  for  ground  water  (Art.  54). 

(7)  Occasionally  it  may  be  necessary  also,  in  the  case  of  certain 
sewers,  to  make  special  allowances  for  manufacturing  sewage  from 
large  factories,  each  factory  being  studied  by  itself  to  determine  its 
probable  sewage  flow.     This  flow  will  usually  be  subject  to  as  much 
fluctuation  as  sanitary  sewage,  and  hence  must  be  multiplied  by  the 
factors  given  in  5,  above. 

(8)  On  the  sewer  profiles  (see  Art.  92),  the  grades  of  the  sewers 
at  the  successive  points  will  be  determined  and  shown.     Using  these 
grades,  and  the  total  maximum  rates  of  flow  of  sewage  determined 


68 


SEWERS  AND  DRAINS 


TABLE  VI 
Sizes  Required  for  Separate  Sanitary  Pipe  Sewers 


DlAM. 

OF 

SEWER. 
INS. 

GRADE 
OF 
SEWER, 

% 

MAXIMUM 
PERMISSIBLE 
Av.  FLOW. 
GALS.  PER 
DAY 

MAXIMUM  PERMISSIBLE 
TRIBUTARY  POPULATION 

MAXIMUM  PERMISSIBLE 
LINEAR  FEET  OF  TRIBUTARY 
SEWER  FOR  20  PERSONS 
PER  100  FEET 

Gals,  per  Capita  per  Day 

Gals,  per  Capita  per  Day 

75 

100 

125 

75 

100 

125 

8 

0.43 
0.60 
0.80 
1  00 
1.40 

130,000 
160,000 
180,000 
200,000 
240,000 

1,700 
2,100 
2,400 
2,700 
3,200 

1,300 
1,600 
1,800 
2,000 
2,400 

1,000 
1,300 
1,400 
1,600 
1,900 

8,700 
11,000 
12,000 
13,000 
16,000 

6,500 
8,000 
9,000 
10,000 
12,000 

5,200 
6,400 
7,200 
8,000 
9,600 

10 

0.30 
0  40 
0.60 
0.80 
1.00 

220,000 
260,000 
310,000 
360,000 
400,000 

2,900 
3,400 
4,100 
4.800 
5.300 

2,200 
2,600 
3,100 
3,600 
4,000 

1,800 
2,100 
2,500 
2,900 
3,200 

15,000 
17.000 
21,000 
24,000 
27,000 

11,000 
13,000 
15,000 
18,000 
20,000 

8,800 
10,000 
12,000 
14,000 
16,000 

12 

0  23 
0.40 
0.60 
0  80 

i!oo 

350,000 
460,000 
560,000 
650,000 
720,000 

4,700 
6,100 
7,500 
8,700 
9,600 

3,500 
4,600 
5,600 
6.500 
7,200 

2,800 
3,700 
4,500 
5,200 
5,800 

23,000 
31.000 
37,000 
43,000 
48,000 

17,000 
23,000 
28,000 
32,000 
36,000 

14,000 
18,000 
22,000 
26,000 
29,000 

15 

0.17 
0.30 
0  40 
0.60 
0.80 

550,000 
750,000 
850,000 
1,000,000 
1,200,000 

7,300 
10,000 
11,000 
13,000 
16,000 

5,500 
7,500 
8,600 
10,000 
12,000 

4,400 
6,000 
6,900 
8.000 
9,600 

37,000 
50,000 
57,000 
67,000 
80,000 

27,000 
37,000 
43,000 
50,000 
60,000 

22,000 
30,000 
34,000 
40,000 
48,000 

18 

0.13 
0  30 
0.40 
0.60 
0.80 

800,000 
1,200,000 
1,400,000 
1,700,000 
2,000,000 

11,000 
16,000 
19,000 
23,000 
27,000 

8,000 
12,000 
14,000 
17,000 
20,000 

6,400 
9,600 
11,000 
14,000 
16,000 

55,000 
80,000 
93,000 
113,000 
134,000 

40,000 
60,000 
70,000 
85,000 
100,000 

32,000 
48,000 
56,000 
68,000 
80,000 

24 

0  10 
0.20 
0.40 
0  60 
0.80 

950,000 
1,300,000 
1,900,000 
2,300,000 
2,600,000 

12,000 
17,000 
25,000 
31,000 
35,000 

9,500 
13,000 
19,000 
23,000 
26,000 

7,400 
10,000 
15.000 
18,000 
21,000 

62.000 
87,000 
126,000 
153,000 
173,000 

46,000 
65,000 
95,000 
115,000 
130,000 

37,000 
52,000 
76,000 
92,000 
104,000 

27 

0.08 
0.20 
0.30 
0.40 
0.60 

1,400,000 
2,200.000 
2,700,000 
3,100,000 
3,800,000 

19,000 
29,000 
36,000 
41,000 
51,000 

14,000 
22,000 
27,000 
31,000 
38,000 

11,000 
18,000 
22,000 
25,000 
30,000 

93,000 
147,000 
180,000 
207,000 
254,000 

70,000 
110,000 
135.000 
155,000 
190,000 

56,000 
88,000 
108,000 
124,000 
152,000 

30 

0.06 
0.10 
0  20 
0.40 
0.60 

2,200.000 
2,800,000 
4,000.000 
5,700,000 
7,000,000 

29,000 
37,000 
53,000 
76,000 
93,000 

22,000 
28,000 
40,000 
57,000 
70,000 

18.000 
22,000 
32,000 
46,000 
56,000 

147,000 
187,000 
267.000 
380,000 
466,000 

110,000 
140,000 
200,000 
285,000 
350,000 

88,000 
112,000 
160,000 
238,000 
280,000 

36 

0.05 
0  10 
0.20 
0.40 
0  60 

3,200,000 
4,600,000 
6,500,000 
9,300,000 
11,400,000 

43,000 
61,000 
87,000 
124,000 
152,000 

32,000 
46,000 
65,000 
93,000 
114,000 

26,000 
37,000 
52,000 
74,000 
91,000 

214,000 
307,000 
433,000 
620,000 
760,000 

160,000 
230,000 
325,000 
465,000 
570,000 

128,000 
184,000 
260,000 
372,000 
456,000 

SEWERS  AND  DRAINS  69 

in  5,  6,  and  7,  above,  refer  to  Fig.  27  for  pipe  sewers,  or  to  Fig.  28  for 
brick  or  concrete  sewers,  and  find  the  sizes  of  sewers  required. 

Example  28.  In  a  town  in  which  the  blocks  are  340  feet,  center  to 
center  of  streets,  there  are  14  lots  per  block.  The  total  length  of  tributary 
sewers  above  a  certain  point  on  a  sub-main  sewer  in  the  system  (separate 
sewers),  is  16,600.  The  conditions  affecting  rate  of  sewage  flow  per  capita  are 
average.  No  allowance  need  be  made  for  ground  water  or  manufacturing  sew- 
age. The  grade  of  the  sewer  is  0.30  per  cent.  What  size  is  required? 

Solution.     The  tributary  population  will  be  ~^-j—  =  25  persons  per  100 

feet  of  sewer.  The  average  rate  of  flow  may  be  assumed  at  85  gallons  per 
capita  per  day.  Hence  the  maximum  rate  of  flow  for  this  sub-main  sewer 
will  be  166  X  25  X  85  X  3i  =  1,150,000  gallons  per  day. 

Hence,  by  Fig.  27,  for  a  0.30  per  cent  grade,  a  12-inch  pipe  sewer  will  be 
required. 

Answer.    A  12-inch  pipe  sewer. 

56.    Table   of  Sizes   Required   for  Sanitary  Sewers.    By  the 

methods  given  in  Art.  55,  omitting  allowances  for  ground  water  and 
manufacturing  sewage,  Table  VI  (page  68)  has  been  computed,  to 
reduce  the  labor  of  computation  of  sizes  of  separate  sanitary  pipe 
sewers. 

TO  USE  THE  TABLE 

Proceed  to  follow  out  steps  1,  2,  3,  and  4,  in  Art.  55,  just  above  (which 
read),  thus  determining  the  total  estimated  future  number  of  linear  feet  of 
tributary  sewer  at  successive  points,  the  estimated  future  number  of  persons 
tributary  per  100  feet  of  sewer  (which  let  =  P),  and  the  estimated  average 
flow  of  sewage  in  gallons  per  capita  per  day  (which  let  =  F).  Also  ascertain 
the  grade  to  which  the  sewer  is  to  be  built. 

(A)  //  P  =  20  persons  per  100  feet,  and  if  F  lies  between  75  and  125 
gallons  per  capita  per  day,  and  if  no  allowance  is  necessary  for  ground  water  or 
manufacturing  sewage,  find  in  column  7,  8,  or  9,  or  by  interpolating  between 
them,  according  to  the  value  of  F,  a,  number  close  to  the  calculated  number  of 
linear  feet  of  tributary  sewer  opposite  to  the  given  sewer  grade,  interpolating 
between  the  grades,  and  take  the  corresponding  size  of  sewer  in  column  1. 

Example  29.  For  13,100  linear  feet  of  sewer,  20  persons  per  100  ft.,  85 
gallons  per  capita  per  day,  and  0.35  per  cent  grade. 

We  find  that  for  a  0.35  per  cent  grade  an  8-inch  sewer  would  be  con- 
siderably too  small,  as  shown  by  interpolating  between  the  numbers  in 
columns  7  and  8,  while  a  10-inch  sewer  would  be  a  little  larger  than  needed. 

Answer.     A  10-inch  pipe  sewer. 

(5)  If  P  does  not  =  20  persons  per  100  feet  (the  other  conditions  re- 
maining as  in  A,  above),  first  multiply  the  number  of  linear  feet  of  tributary 

p 
sewer  by  —  ,  and  then  proceed  as  in  A ,  just  above. 


70  SEWERS  AND  DRAINS 

Example  30.  For  16,300  linear  feet  of  sewer,  30  persons  per  100  feet  of 
sewer,  110  gallons  per  capita  per  day,  and  a  sewer  grade  of  0.25  per  cent. 

OQ 

We  first  find  16,300  X—  =  24,450  linear  feet.  Then  interpolating  be- 
tween columns  8  and  9,  we  find  that  for  a  0.25  per  cent  grade  a  12-inch  would 
be  considerably  too  small,  while  a  15-inch  sewer  is  a  little  larger  than  needed, 

Answer.     A  15-inch  pipe  sewer. 

(C)  If  F  (rate  of  sewage  flow)  is  less  than  75  or  more  than  125  gallons  per 
capita  per  day,  first  multiply  the  number  of  linear  feet  of  tributary  sewer  by 

jf  P* 

---  ,  and  then  by-—-  (where  P  =  persons  per  100  feet  of  sewer),  and  then  find 

the  nearest  number  in  column  8  opposite  the  given  grade. 

Example  31.  For  22,500  linear  feet  of  sewer,  35  persons  per  100  feet, 
150  gallons  per  capita  per  day,  and  0,45  per  cent  grade. 

We  first  find  22,500  X  ^  X  ||-  =  59,000  linear  feet,.     In  column  8  we 

find  that  for  a  0.45  per  cent  grade  a  15-inch  sewer  would  be  considerably  too 
small,  while  an  18-inch  is  too  large. 

Answer.     An  18-inch  pipe  sewer. 

(D)  If  ground  water  or  manufacturing    sewage,  or  both,  must  be  allowed 
for,  ascertain  the  total  average  sewage  flow,  by  multiplying  the  linear  feet  of 

p 

tributary  sewer  by  -  -  (P  =  persons  per  100  feet),  and  this  result  by  F  (=  gal- 
lons per  capita  per  day,  of  sanitary  sewage),  and  by  then  adding  to  this  result 
the  total  allowance  for  manufacturing  sewage,  and  ^  the  total  allowance  for 
ground  water.  Then  find  by  interpolation  in  column  3  the  nearest  number 
opposite  the  given  grade,  and  take  the  corresponding  size  of  sewer. 

Example  32.  For  15,600  linear  feet  of  tributary  sewer,  25  persons  per 
100  feet,  85  gallons  per  capita  per  day,  15,000  gallons  per  day  per  mile  ground 
water,  200,000  gallons  per  day  manufacturing  sewage,  and  0.20  percent  grade. 

25 

We  find  the  total  average  flow  of  sewage  to  use  is  15,600  X  rnx  X  85  -f 

1UU 

i  c  oon 

200,000  -\ 1     -  X  3  (miles)  =  546,000  gallons  per  day.  In  column  3  we  find 

3 

that  for  a  0-20  per  cent  grade,  a   12-inch   sewer  would  be  considerably  too 
small,  while  a  15-inch  is  a  little  larger  than  is  needed. 
Answer.     A  15-inch  pipe  sewer. 

GENERAL  EXAMPLE   FOR  PRACTICE   IN   DESIGNING   SEPARATE 
SANITARY   SEWERS 

57.  Working  out  the  following  example  will  materially  help 
the  student. 

Example  33.  Calculate  the  size  of  the  outlet  sewer  of  the  sewer  system 
shown  in  Fig.  4,  assuming  that  there  will  be  in  the  future  20  persons  tributary 
per  100  feet  of  sewer,  that  the  average  flow  of  sewage  will  be  100  gallons  per 
capita  per  day,  no  special  allowance  for  ground  wat,er  or  manufacturing  sew- 
age being  needed.  Also  assume  that  there  may  be  in  the  future  15,000  feet 
of  sewer  extensions  not  shown  in  the  figure.  The  grade  of  the  outlet  sewer  is 
0.20  per  cent.  Assume  scale  of  drawing,  1,500  feet  per  inch. 


SEWERS  AND  DRAINS  71 

Solution.  Take  a  long  strip  of  paper  with  one  edge  straight;  and  on 
this,  mark  off  with  a  pencil  a  scale  of  feet  from  the  scale  assumed  above. 
With  this,  scale  off  the  lengths  of  all  the  sewers  shown,  except  the  storm 
sewers.  Add  up  the  lengths  scaled,  and  add  15,000  linear  feet  of  future  ex- 
tensions, to  get  the  total  length  of  tributary  sewer.  Then  use  Table  VI. 

Answer.     An  18-inch  pipe  sewer. 

CALCULATION  OF  SIZES  AND  MINIMUM  GRADES  OF 
STORM  AND  COMBINED  SEWERS 

58.    Storm  and  Combined  Sewers  Calculated  by  Same  Methods. 

In  combined  sewers  the  rate  of  flow  of  sanitary  sewage  is  so  small  in 
time  of  storms  in  proportion  to  that  of  the  storm  sewage,  that  the 
sanitary  sewage  can  be  neglected  altogether  in  calculating  the  size. 
For  example,  a  combined  sewer  one  mile  long,  with  20  persons  tribu- 
tary per  100  feet,  and  75  gallons  per  capita  per  day,  would  have  a 
maximum  rate  of  flow  of  sanitary  sewage  at  its  lower  end  of 
52.8  X  20  X  75  X  3J 

7*  X  86  400  ~~  =  CU*  per  second  (there  bemS  7^  &als* 

in  1  cu.  ft.,  and  86,400  seconds  in  1  day,  and  the  maximum  rate  of 
flow  being  3J  times  the  average). 

If  the  blocks  are  360  feet  wide,  center  to  center  of  streets,  this 
same  sewer  would  have  to  take  the  storm  sewage  from  43J  acres. 
The  amount  of  this  at  the  time  of  the  maximum  storm  allowed  for, 
calculated  by  the  methods  described  below,  would  probably  be  at 
least  20  cu.  ft.  per  second.  The  sanitary  sewage  would  therefore  be 
only  about  2  per  cent  of  the  storm  sewage.  The  amount  of  the  latter 
cannot  be  foretold  nearly  so  close  as  2  per  cent.  Thus  the  sanitary 
sewage  would  have  no  appreciable  effect  upon  the  size  of  the  com- 
bined sewer,  and  can  be  neglected. 

59;  Minimum  Sizes  of  Storm  and  Combined  Sewers.  In  the 
case  of  sanitary  sewers,  8  inches  was  stated  to  be  the  minimum  allow- 
able diameter  (see  Art.  47) ;  but  in  the  case  of  sewers  carrying  storm 
sewage,  there  is  much  greater  danger  of  stoppages  from  dirt,  sticks,  and 
other  debris  washed  in  from  the  surface  during  storms.  Hence 
twelve  inches  should  be  the  minimum  allowable  diameter  for  storm  and 
combined  sewers. 

60.  Minimum  Grades  and  Velocities  for  Storm  and  Combined 
Sewers.  It  was  stated  in  connection  with  sanitary  sewers  (Art.  48), 
that  the  minimum  allowable  velocities  to  prevent  deposits  should  be 


72 


SEWERS  AND  DRAINS 


TABLE  VII 
Minimum  Grades  for  Storm  and  Combined  Sewers 


SHAPE 

MATERIAL 

SIZE 

MINIMUM  GRADES  TO  GIVE 
VELOCITIES  OF 

3  FT.  PER   SEC.  '4  FT.  PER   SEC. 

Circular 

Pipe 

12-in.  D 
15 

am. 

0.48 

0.34 

0.88 
0.62 

7 

7) 

18 

0.25 

0.47 

' 

77 

24 

0.17 

0.31 

' 

» 

30 

0.13 

0.23 

' 

Brick  or  Concrete 

3-ft. 

0.14 

0.25 

f 

» 

4 

0.10 

0.17 

7 

7 

5 

0.07 

0.12 

| 

7 

6 

0.06 

0.10 

7 

7 

7 

0.05 

0.08 

> 

7 

8 

0.04 

0.06 

7 

' 

9 

0.03 

0.05 

) 

' 

10 

0.025 

0.045 

Egg-S 

iaped 

' 

2    ft.  X     3    ft. 

0.20 

0.35 

77 

2}'     X     3f    ' 

0.15 

0.26 

" 

3         X     4i    ' 

0.12 

0.20 

J> 

4          X     6 

0.08 

0.14 

77 

5         X     7J     ' 

0.06 

0.10 

" 

6         X     9      ' 

0.05 

0.08 

77 

7         X  10} 

0.04 

0.07 

1 J  feet  per  second  at  the  minimum  depths  of  flow,  which  will  require 
grades  sufficient  to  give  minimum  velocities  of  2  feet  per  second  when 
the  sewer  flows  full  or  half-full.  For  sewers  carrying  storm  sewage, 
however,  greater  minimum  velocities  are  necessary  to  prevent  deposits, 
on  account  of  the  dirt,  pebbles,  and  other  heavy  rubbish  washed  into 
them  from  the  surface  in  times  of  storms.  For  combined  and  storm 
sewers  the  minimum  allowable  grades  should  be  steep  enough  to  give  a 
minimum  velocity  of  3  feet  per  second.  If  practicable  without  too  great 
expense,  4  feet  per  second  should  be  secured. 

61.  General  Explanation  of  the  Calculation  of  Amount  of  Storm 
Sewage.  When  rain  begins  to  fall  upon  the  area  drained  by  a  storm 
sewer,  the  water  falling  in  the  immediate  neighborhood  of  the  outlet 
at  once  enters  the  sewer  and  begins  to  be  discharged.  As  time  passes 
and  the  rain  continues,  water  arrives  at  the  outlet  from  more  and 
more  remote  portions  of  the  drainage  area,  and  the  discharge  at  the 
outlet  increases  quite  rapidly  until  water  is  being  discharged  from  all 
portions  of  the  drainage  area  at  the  same  time.  After  that,  any 
further  increase  is  slow,  being  due  only  to  a  per  cent  of  run-off  slowly 
increasing  as  the  saturation  cf  the  soil  becomes  more  complete. 


SEWERS  AND  DRAINS 


73 


The  time  of  concentration  is  the  longest  time  required  for  water 
from  the  remotest  points  of  the  portion  of  the  drainage  area  being 
considered,  to  reach  the  outlet  of  that  portion. 

The  general  law  of  the  heaviest  rainfalls,  the  ones  which  determine 
the  sizes  of  sewers,  is  that  the  heaviest  rates  for  short  storms  are  much 
greater  than  the  heaviest  rates  for  long  storms.  The  longer  the  time, 
the  less  will  be  the  average  rate  of  the  maximum  storm  lasting  that  time. 

In   Fig.  33,  is  given  a  diagram 
prepared  by  Prof.    A.   N.  Talbot, 
showing  rainstorms  in  the  Central 
States.      On  this  diagram  the  or- 
dinates  represent  the  rate  of  rainfall 
in  inches  per  hour  (which  =  cu.  ft. 
per  second  per  acre),  while  the  ab- 
scissse  represent  the  duration  of  the 
storm.       Three    curves    are    also 
shown,  one  for  very  rare  rainfalls, 
one  for  ordinary 
heavy  rains,  and 
one   intermedi- 
ate.   On  the  dia- 
g  r  a  m    each    + 
represents    o     e 
storm. 

The  storm 
causing  the  great- 
est rate  of  dis- 
charge in  a  storm 
sewer  will  us- 
ually be  the  max- 
imum rain  last- 
ing a  length  of 

time  equal  to  the  time  of  concentration.  If  a  time  less  than  this  be 
taken,  water  will  not  be  discharged  at  the  outlet  from  all  parts  of  the 
drainage  area  at  once,  and  that  from  near  the  outlet  will  have  a  chance 
to  run  away  before  that  from  the  remotest  points  arrives.  On  the 
other  hand,  if  a  time  be  taken  longer  than  the  time  of  concentration, 
the  heaviest  rate  of  the  maximum  storm  lasting  this  long  will  be  less 


2O       4O      2>rrs   2O       AO      3Vrs    20  3O 
of  Storm  ITI  Mirvu.tes 

Fig.  33.    Rates  of  Heavy  Rainfall  in  the  North  Central  States, 
Ohio,  Indiana,  Illinois,  Missouri,  Kansas,  and  Iowa. 


74  SEWERS  AND  DRAINS 

than  the  rate  of  the  maximum  storm  lasting  a  length  of  time  just 
equal  to  the  time  of  concentration;  and  since  the  storm  is  lighter  the 
flow  will  be  lighter. 

Not  all  of  the  water  falling  on  a  drainage  area  will  be  carried 
away  in  the  sewer.  During  and  after  the  storm,  some  of  the  water  is 
evaporated  into  the  air,  and  some  is  absorbed  into  the  soil.  Some 
also  accumulates  on  the  surface,  to  flow  off  into  the  sewer  after  the 
rain  has  ended.  The  engineer  determines  the  percentage  of  the  rain 
ftowing  off  in  the  sewer,  by  estimating  the  percentage  0}  maximum  run- 
off of  the  drainage  area. 

The  general  method  for  calculating  the  amount  of  storm  sewage  for 
any  particular  drainage  area,  is  therefore  as  follows : 

(a)  Calculate  the  time  of  concentration,  or  longest  time  of  flow  to  the 
point  for  which  the  size  of  sewer  is  being  determined. 

(6)  Calculate  the  rate  of  maximum  rainfall  corresponding  to  the  time 
of  concentration. 

(c)  Calculate  the  percentages  of  impervious  and  pervious  areas  on  the 
watershed  drained  by  the  sewer. 

(d)  Using  the  percentages  of  impervious  and  pervious  areas  obtained  in 
c,  calculate  the  maximum  percentage  of  run-off,  or  the  percentage  of  the  rate  of 
the  maximum  rainfall  which  will  be  running  off  in  the  sewer  under  design  at 
the  end  of  the  time  of  concentration. 

(e)  Calculate  the  total  maximum  rate  of  flow  of  storm  sewage,  by  multi- 
plying together  the  drainage  area,  tfre  maximum  rate  of  rainfall  corresponding 
to  the  time  of  concentration,  and  the  maximum  percentage  of  run-off. 

62.  Calculation  of  the  Time  of  Concentration.  The  time  of 
concentration,  which  is  the  longest  time  required  for  water  falling 
on  the  remote  portions  of  the  watershed  to  flow  to  the  point  for  which 
the  size  of  sewer  is  being  determined,  will  be  the  sum  of,  (1),  the  time 
required  for  the  water  from  roofs,  yards,  sidewalks,  and  pavements  to 
reach  the  sewers  by  way  of  the  gutter  and  street  inlets,  and,  (2),  the 
longest  time  required  for  the  water  to  flow  through  a  line  of  sewers  to 
the  point  for  which  the  size  of  sewer  is  being  calculated. 

(1)  Time  Required  for  Water  from  Roofs,  Gutters,  etc.,  to  Reach 
the  Sewers.  This  will  usually  be  between  the  limits  of  5  and  15  minutes, 
depending  on  the  steepness  of  the  slopes  of  the  surface  and  of  the 
gutters,  on  the  distance  the  water  must  flow  to  reach  the  gutters  and 
the  distance  it  must  flow  in  the  gutters  to  reach  the  street  inlets,  on 
the  character  of  the  surface  (whether  it  offers  obstructions  to  flow  or 
not),  or  whether  the  roofs  are  connected  to  the  gutters  or  directly  to 


SEWERS  AND  DRAINS  75 

the  sewers,  etc.  By  looking  over  the  ground  carefully,  and  allowing 
for  the  above  conditions  in  a  general  way,  the  time  may  be  estimated 
as  closely  as  the  data  will  warrant,  without  special  calculations.  The 
upper  limit  of  15  minutes  may  be  used  when  the  gutters  have  a  very 
light  grade,  and  are  two  blocks  long,  and  where  the  roofs  discharge 
into  the  gutters  instead  of  into  the  sewer  direct. 

(2)  Longest  Time  Required  for  the  Water  to  Flow  through  the 
Sewers.  This  is  computed  by  taking  the  grades  and  sizes  of  the 
different  parts  of  usually  the  longest  line  of  sewers,  and  determining 
the  corresponding  velocities  of  flow  by  the  use  of  the  sewer  diagrams, 
Figs.  27,  28,  and  29,  already  given.  From  these  velocities,  and  the 
lengths  of  the  several  portions  of  the  sewer,  the  corresponding  times 
required  for  the  sewage  to  flow  through  each  part  can  be  readily 
computed,  and  their  sum  will  be  the  time  required.  The  designing 
must  be  begun  at  the  upper  ends  of  the  sewers,  so  that  we  may  know 
the  sizes  of  sewer  needed  in  computing  the  times  of  flow  through 
each  portion. 

Example  34.  Required  the  time  of  concentration  in  the  following 
case:  The  longest  sewer  consists  of  400  feet  of  18-inch  pipe  sewer, 
grade  0.5  per  cent;  800  ft.  of  24-inch  pipe,  grade  0.3  per  cent; 
1,200  ft.  of  36-inch  brick  sewer,  grade  0 . 25  per  cent;  2,400  ft.  of  48-inch 
brick  sewer,  grade  0.17  per  cent.  The  roofs  discharge  into  the 
gutters,  through  which  the  sewage  must  flow  2  blocks  at  0 . 5  per  cent 
grade  to  reach  a  street  inlet. 

Solution : 
Estimated  for  water  from  roofs  Velocity  Time 

and  gutter  to  reach  sewer  15.0     min. 

In  18-inch  sewer,  Fig.  27  4 . 2  ft.  per  sec.  1.6       " 

"  24-inch      "        "27  4.0  "    "    "  3.3      " 

"  36-inch      "        "    28  4.0  "     "    "  5.0       " 

"48-inch      "        "    28  4.0"    "     "  jmJO       " 

Answer.     Total  time  of  concentration  =  35 

63.  Calculation  of  the  Rate  of  Rainfall  Corresponding  to  the 
Time  of  Concentration.  In  Fig.  34  are  reproduced  separately  the 
three  rainfall  curves  shown  in  Fig.  33.  Storms  of  the  1st  and  2d 
classes  are  rare,  and  are  so  very  heavy  that  it  would  be  excessively 
expensive  to  build  sewers  large  enough  for  them.  Hence  sewers  are 
usually  built  only  large  enough  to  provide  for  storms  of  the  3d  class, 


76 


SEWERS  AND  DRAINS 


It  is  considered  less  expensive  to  suffer  some  damage  from  rare 
overcharging  of  the  sewers  than  to  build  the  greater  sizes,  though  in 
case  very  valuable  property  would  be  damaged  it  may  be  wiser  to 
provide  for  the  heaviest  storms. 

TO  USE  THE  DIAGRAM 

Find  the  time  of  concentration  at  the 
bottom  of  the  diagram.  Vertically  over 
it,  on  the  curve  for  storms  of  the  3d  class 
(unless  greater  storms  are  to  be  provided 
for),  locate  a  point;  and  horizontally 
opposite  this,  read  off  on  the  left  the 
rate  of  rainfall. 

Example  35.  Find  the  rate  of 
rainfall  to  use  in  example  34. 

Solution.  The  time  of  concen- 
tration is  35  min.  Over  this  we  read 
on  the  curve  for 
3d-class  storms, 
2 . 1  inches  per 
hour. 

Answer.  2 . 1 
inches  per  hour. 

64.  Calcula= 
tion  of  the  Per= 
centages  of  Im= 
pervious  and 
Pervious  Areas 
on  the  Sewer 

£=Durationofstorminminutes=Timeof  concentration=Time 

required  for  water  to  flow  from  the  remotest  part  of  the  area  Watershed.  I  he 
drained  to  the  point  under  consideration  on  the  sewer. 

Fig.  34.    Diagram  Showing  Rates  of  Maximum  Rainfall  to  be  Used    percentage     of 
in  Calculating  the  Size  of  Storm  Sewers. 

impervious  area 
may  be  calculated  in  the  following  manner: 

Take  a  typical  unit  of  area,  usually  one  average  block,  and 
divide  it  into  different  classes  of  surfaces,  having  different  percentages 
of  imperviousness,  as  follows: 

(a)  Roof  Area.  From  the  average  size  of  buildings,  and  the 
average  number  of  buildings  per  block  which  will  be  connected  w'th 


3hr.s     20  3d 


SEWERS  AND  DRAINS  77 

the  sewers  or  with  the  gutters,  calculate  the  total  roof  area  in  the 
block.  Take  this  at  its  full  value  if  the  roofs  are  connected  directly 
with  the  sewers,  but  take  only  90  per  cent  if  the  roofs  are  connected 
with  the  gutters. 

(b)  First-Class  Pavements.     Calculate  the  total  area,  per  block, 
of  brick,  asphalt,  stone  block,  and  similar  first-class  pavements,  with 
tight  joints,  and  take  80  per  cent  of  this  area. 

(c)  Second-Class  Pavements.     Calculate  the  total  average  area 
per  block,  and  take  60  per  cent. 

(d)  Third-Class  Pavements.      Calculate  the  total  average  area 
per  block  of  good  macadam  and  similar  pavements,  and  take  40 
per  cent. 

(e)  Hard-Earth  Roads.     Calculate  the  total  average  area  per 
block  of  the  traveled,  hard-earth  surfaces,  and  take  20  per  cent. 

(/)  Sidewalks.  Calculate  the  several  total  average  areas  per 
block  of  1st,  2d,  and  3d-class  sidewalks,  corresponding  to  the  classes 
of  pavements  in  b,  c,  and  d,  above.  If  these  extend  to  the  gutters, 
as  in  business  districts,  take  the  same  percentages  as  for  the  corres- 
ponding classes  of  pavements — namely,  80,  60,  and  40  per  cent  for 
1st,  2d,  and  3d-class  sidewalks,  respectively.  But  if  the  pavements 
are  separated  from  the  gutters  by  wide  parking,  as  in  the  residence 
districts,  take  only  one-half  the  above  percentages — namely,  take  40, 
30,  and  20  per  cent,  for  1st,  2d,  and  3d-class  sidewalks,  respectively. 

Finally,  add  together  all  the  reduced  average  areas  per  block  (a,  b, 
c,  d,  e,  and  f )  obtained  as  above  explained,  and  divide  the  sum  by  the 
total  area  of  the  typical  block.  The  quotient  will  give  the  percentage 
o]  impervious  area. 

The  percentage  of  pervious  area  is  obtained  by  subtracting  the  per- 
centage o]  impervious  area  from  100  per  cent. 

Example  36.  In  examples  34  and  35,  assume  the  typical  block 
to  be  360  ft.  square,  center  to  center  of  streets,  as  follows: 

Streets,  60  ft.  wide;  pavements,  30  ft.  wide;  asphalt  on  two 
streets;  good  macadam  on  the  other  two;  cement  sidewalks,  5  ft.  wide, 
on  all  four  streets. 

One  alley  20  ft.  wide. 

Lots,  12  in  number,  each  50  X  140  ft.,  each  lot  containing  one 
house,  the  houses  averaging  30  X  40  ft.,  the  roofs  connected  with  the 
gutter. 


78 


SEWERS  AND  DRAINS 


Calculate  the  percentage  of  impervious  and  pervious  area. 
Solution : 

30  X  40  X    12  X  .90  =  12,960  sq.  ft. 
2  X  15  X  360  X  .80  =     8,640 
2X  15X330  X  .40=     3,960       " 
5  X  1,210  X  .40         =     2,420       " 

Total  impervious  area  per  block  =  27,980  sq.  ft. 

Total  area  of  one  block  =  360  X  360  =  129,600  sq.  ft. 

27  ggQ 
Percentage  of  impervious  area  =  1  on^nr>  =  21 . 58  per  ct. 


(a)  Roofs, 

(6)  Ist-Class  Pavements, 

(d)  3d-Class  Pavements, 

(/)  1  st-Class  Sidewalks, 


Answer. 


129,600 

Percentage  of  pervious  area  =100  — 21 . 58  =  78 . 42  per  cent. 
Mr.  Emil  Kuichling,   M.  Am.  Soc.  C.  E.,  has  calculated  the 
percentages  of  impervious  area  in  various  cities  of  New  York  State, 
and  his  wofk  has  been  repeated  by  Prof.  H.  N.  Ogden,*  who  finds 
the  percentage  to  vary  with  the  intensity  of  population,  as  follows: 

TABLE  VIII 
Approximate  Percentages  of  Impervious  Area  in  Cities 


POPULATION  PER  ACRE 

PERCENTAGE  OF  IMPERVIOUS 
AREA 

PERCENTAGE  OF  PERVIOUS 
AREA 

5 

4 

96 

10 

9* 

90* 

15 

15 

85 

20 

20* 

79* 

25 

26 

74 

30 

31* 

68* 

35 

37 

63 

40 

42* 

57* 

45 

47* 

52* 

50 

52* 

47* 

55 

58 

42 

Even  very  heavily  populated  sections  in  the  largest  cities  will 
seldom  have  more  than  80  to  85  per  cent  of  impervious  area. 

Table  VIII  furnishes  an  easy  method  of  making  approximate 
estimates  of  the  percentages  of  impervious  area. 

Example  37.  In  example  36,  estimate  the  percentage  of  imper- 
vious area  by  Table  VIII. 

Solution.    The    typical    block    contains    129,600    sq.    ft.;   and 

129,600  (sq.  ft.) 

/      ft  N  =  3  acres.     The   12  houses   at   an   average   of    5J 

persons  per  house,  would  give  66  persons  per  block  =  22  per  acre. 

*  Sewer  Design,  p.  62. 


SEWERS  AND  DRAINS  79 

Referring  to  Table  VIII  we  find  by  interpolating,  22}  per  cent 
of  impervious  area,  as  compared  with  21.6  per  cent  obtained  above 
by  the  more  exact  method. 

65.  Calculation  of  the  Maximum  Percentage  of  Run=0ff.  Not 
all  of  the  rain  falling  on  the  impervious  area  of  a  watershed  will  run 
off  during  the  storm.  Small  amounts  are  evaporated  or  absorbed 
at  once,  for  no  city  surfaces  are  absolutely  impervious.  A  larger 
amount  goes  to  fill  up  small  depressions  in  the  surfaces.  A  still 
larger  amount  accumulates  on  the  surfaces  of  the  watershed,  making 
its  way  toward  the  sewer,  the  amount  so  accumulated  and  its  rate 
of  movement  increasing  as  the  storm  continues  at  the  same  rate,  until 
finally  an  equilibrium  of  flow  is  established,  and  the  rate  of  the  run-off 
from  the  impervious  area  becomes  practically  100  per  cent  of  the 
rainfall.  Thus,  the  shorter  the  storm,  the  less  the  percentage  of 
run-off  from  the  impervious  area;  and  hence  sewer  watersheds  having 
the  smallest  times  of  concentration  are  likely  to  have  the  smallest 
percentages  of  maximum  run-off  from  the  impervious  areas. 

The  maximum  downpours  which  determine  the  size  of  the 
sewer,  are  often  preceded  by  lighter  downpours  which  saturate  and 
partially  flood  the  watershed.  Hence  it  will  probably  never  be  allow- 
able to  assume  less  than  75  per  cent  as  the  percentage  of  maximum 
run-off  from  the  impervious  areas  of  a  sewer  watershed,  even  with  very 
short  times  of  concentration,  and  comparatively  little  damage  from 
overcharged  sewers. 

With  long  times  of  concentration  (say  45  minutes  or  more),  and 
wherever  great  damage  would  be  caused  by  overcharged  sewers, 
100  per  cent  of  maximum  run-off  from  the  impervious  areas  should  be 
assumed. 

In  the  case  of  long-continued  storms,  the  pervious  area  becomes 
gradually  saturated,  until  some  run-off  occurs  from  it  also.  In  the 
case  of  storms  lasting  several  hours,  such  as  cause  the  great  floods  in 
rivers,  this  percentage  of  maximum  run-off  may  be  quite  high;  but 
for  sewers,  the  times  of  concentration,  and  hence  the  duration  of  the 
maximum  downpour,  are  comparatively  short — rarely  as  long  as  one 
hour. 

For  soils  of  average  porosity  and  for  moderate  slopes,  the  per- 
centage of  maximum  run-off  from  the  pervious  areas  may  be  assumed 
to  range  from  0,  for  15  minutes  time  of  concentration,  to,  say,  20  for  I 


80  SEWERS  AND  DRAINS 

hour's  time  of  concentration.  For  porous,  sandy  soils  and  flat  slopes, 
assume  0  to  50  per  cent,  and  for  very  impervious  soils  and  very  steep 
slopes,  125  to  150  per  cent  of  the  above  percentages  of  maximum  run- 
offs from  pervious  areas. 

Example  38.  In  examples  36  and  37,  assume  that  the  territory 
is  a  residence  district,  with  moderate  slopes  and  clay  subsoil.  Esti- 
mate the  percentage  of  maximum  run-off. 

Solution.  Since  the  time  of  concentration  is  only  35  minutes, 
while  the  damage  from  overcharged  sewers  would  not  be  so  great 
as  in  a  business  district,  we  shall  assume  90  per  cent  maximum  rate 
of  run-off  from  the  impervious  area.  For  the  pervious  area,  we 
interpolate  roughly  between  0  per  cent  for  15  minutes,  and  17  per  cent 
for  1  hour,  and  assume  8  per  cent  maximum  rate  of  run-off. 

.  90  X  21 . 6  per  cent  =  19.4  per  cent  from  impervious  area. 
.08X78.4     "      "=J).3     "      "      "      pervious 

Answer.  Total  =  26    per  cent  maximum  rate  of  run-off. 

66.  Summary  of  Methods  of  Computing  Sizes  of  Storm  Sewers. 
We  may  now  summarize  the  methods  of  computing  the  sizes  of  storm 
sewers,  described  above  in  Articles  61  to  65,  inclusive,  as  follows: 

(a)  Calculate  the    time   of   concentration  (Art.  62),  or  longest  time  of 
flow  from  the  remote  portions  of  the  sewer  watershed  to  the  point  for  which 
the  size  of  sewer  is  being  calculated. 

(b)  Calculate  the  maximum   rate  of  rainfall  (Art.  63)  corresponding  to 
the  time  of  concentration. 

(c)  Calculate  the  percentages  of  impervious  and  pervious  areas  on  the 
sewer  watershed  (Art.  64). 

(d)  From  the  percentages  of  impervious  and  pervious  areas,  and  knowl- 
edge of  the  characteristics  of  the  sewer  watershed,  calculate  the  percentage  of 
maximum  run-off  (Art.  65). 

(e)  Calculate  the  maximum  rate  of  flow  of  storm  sewage,  by  multiplying 
together  the  area  of  the  sewer  watershed  in  acres,  the  maximum  rate  of  rainfall  in 
inches  per  hour  (6),  and  the  percentage  of  maximum  run-off  (d).     The  product 
will  be  the  cubic  feet  per  second  of  maximum  storm  sewage  flow. 

(/)  Knowing  the  grade  of  the  sewer,  refer  to  Fig.  27,  or  Fig.  28,  or  Fig.  29, 
according  to  the  shape  and  material  of  the  sewer,  and  determine  the  size  of 
sewer  required  to  carry  the  maximum  flow  of  storm  sewage  (e)  when  flowing 
full. 

Example  39.  In  examples  34  to  38,  assume  that  the  sewer 
watershed  is  5,280  feet  long  by  800  feet  wide,  and  that  the  grade  of 
the  circular  brick  outlet  sewer  is  to  be  0. 15  per  cent.  Calculate  the 
required  diameter. 


SEWERS  AND  DRAINS  81 

(a)  The  time  of  concentration  =  35  min.  (see  Ex.  34). 

(b)  The  rate  of  maximum  rainfall  ==  2  .  1  in.  per  hr.  (see  Ex.  35).  * 
(d)    The  percentage  of  maximum  run-off  =  26  (see  Ex.  38). 

,  x    mi  5,280  X  800 

(*)    The  drainage  area  =  -'  —  =  97  acres. 


97   X   2.1   X    .26   =   53  cu.  ft.  per  sec. 
=    maximum   flow  of  storm   sewage. 

(/)  Referring  to  Fig.  28,  we  find,  by  interpolating  between  the  4-toot 
and  5-foot  diameters,  that  for  a  grade  of  0.15  per  cent  a  diameter  of 
4  ft.  3  in.  will  be  required  for  a  circular  brick  sewer  which  can  carry 
53  cu.  ft.  per  sec. 

Answer.    A  4  ft.  3  in.  circular  brick  sewer. 

GENERAL  EXAMPLE  FOR  PRACTICE 

67.  Before  proceeding  further,  the  student  should  work  out 
the  following  example  in  computation  of  the  proper  size  of  sewer: 

Example  40.  A  thickly  built-up  sewer  district,  having  a  popu- 
lation of  35  persons  per  acre,  jjntains  160  acres.  The  slopes  are  very 
flat,  and  the  soil  is  sandy  and  porous.  The  longest  line  of  sewers  is 
6,000  feet;  and  the  velocity  of  flow  in  the  sewers  averages  four  feet 
per  second.  The  roofs  are  connected  with  the  gutters,  in  which  the 
longest  flow  is  two  blocks.  Calculate  the  diameter  of  the  circular, 
brick  outlet  sewer,  laid  to  a  0.08  per  cent  grade  (NOTE:  Use  Table 
VIII.) 

Answer.     A  6-foot  circular  brick  sewer. 


PARSONS  TRENCH  EXCAVATOR   CUTTING   A    15-FOOT   DITCH  IN   A    14V2-FOOT 

ALLEY 

Courtesy  of  G.  N.  Parsons  Company,  Newton,  Iowa 


SEWERS  AND  DRAINS 

PART  II 


LAND  DRAINS  AND  SUBDRAINS 

68.  General  Discussion  of  Land  Drains.     Definitions  of  sewers 
and  drains  were  given  in  Art.  1.     Land  drains  have  for  their  object 
the  reclaiming  of  wet  lands,  to  render  them  suitable  for  cultivation. 
The  reclamation  of  wet  lands  also  greatly  improves  the  sanitary 
condition  of  the  vicinity. 

There  are  two  principal  kinds  of  land  drains — namely,  tile 
drains,  or  lines  of  agricultural  drain  tiles  laid  a  few  feet  beneath  the 
surface  of  the  ground,  to  remove  ground  water;  and  drainage  ditches, 
or  open  channels,  made  to  serve  as  outlets  for  the  tile  drains  and  to 
drain  ponds  and  remove  surface  water. 

69.  Planning   and   Construction    of   Land=Drainage   Systems. 
When  a  tile  drainage  system  is  projected,  a  competent  drainage 
engineer  should  at  once  be  engaged  to  do  the  necessary  surveying, 
plan  the  system,  and  pass  on  the  construction. 

The  surveying  will  include  the  obtaining  of  data  for  a  complete 
map  of  the  system;  and  each  drain  should  be  staked  out,  stakes  being 
set  50  feet  apart,  and  an  elevation  taken  with  a  good  level  at  each 
stake.  All  the  work  should  be  checked. 

The  engineer  should  then  prepare  for  the  landowner  a  com- 
plete map  of  the  system,  to  a  scale  of  200  to  400  feet  per  inch;  also 
a  sheet  of  profiles,  including  a  profile  of  each  drain,  showing  the 
depth  and  grade  at  all  points.  Without  such  map  and  profiles, 
knowledge  of  the  system  may  be  lost,  and,  on  some  future  occasion, 
when  very  badly  needed,  may  be  unavailable. 

The  engineer  should  plan  as  simple  and  regular  a  tile  system  as 
possible,  adopting  long,  parallel,  straight  lines  of  tile  when  practicable, 
with  as  few  junctions  as  possible. 

The  grades  may  be  very  light  in  case  of  necessity,  and  short  tile 
drains  have  worked  well  even  at  level  grades;  but  the  lighter  the 
grade,  the  greater  should  be  the  care  used  in  construction. 


84  SEWERS  AND  DRAINS 

The  minimum  depths  should  usually  be  3i  to  4  feet.  Shallower 
depths  do  not  drain  out  the  soil  so  thoroughly;  and  tile,  if  laid  3J  to  4 
feet  deep,  can  be  placed  farther  enough  apart  to  more  than  make  up 
for  the  cost  of  the  greater  depth. 

The  lines  of  tile  should  usually  be  placed  from  five  to  ten  rods 
apart,  depending  on  the  soil — farthest  apart  in  the  most  porous  soil. 
The  outlet  should  be  built  with  special  care;  and  a  masonry  wall 
should  be  constructed  to  hold  the  last  length  of  tile. 

For  drainage  ditches,  careful  surveys  of  the  entire  watershed 
must  be  made  by  a  very  competent  engineer;  and  fully  detailed  plans 
and  specifications  must  be  prepared. 

70.  Contracts  and  Specifications  for  Tile  Drains.  The  em- 
ployer and  the  tile  ditcher  should  sign  a  printed  contract  with  detailed 
specifications,  such  as  given  herewith: 

CONTRACT 

It  is  hereby  agreed  between , 

employer,  and ,  contractor, 

that  the  contractor  shall,  except  for  the  furnishing  of  the  tile  along  the  ditch 
and  the  refilling  of  the  ditch,  entirely  construct  for  the  employer  the  following 
described  drains: 


It  is  further  agreed  that  for  the  above  work  the  employer  shall  pay  the 
following  prices: 


It  is  further  agreed  that  the  employer 

furnish  board  free  to  the  contractor  and  his 

helpers  during  active  prosecution  of  the  work. 

It  is  further  agreed  that  the  contractor  shall  begin  the  work  by 

and  complete  the  same  by 

It  is  further  agreed  that  all  the  above  work  and  the  payments  therefor 
shall  be  in  strict  accordance  with  the  specifications  given  below  and  with  the 
engineer's  maps,  profiles,  and  plans,  all  of  which  are  hereby  made  a  part  of  this 
contract. 

Witness  the  hands  of  the  respective  parties,  this day  of 

A.  D 

Employer 

Contractor 


SEWERS  AND  DRAINS  85 

SPECIFICATIONS 

1.  Staking  Out  the  Work.     The  work  will  be  staked  out  by  the  engineer, 
and  his  stakes  must  be  carefully  preserved  and  followed. 

2.  Digging  the  Ditches.     The  digging  of  each  ditch  must  begin  at  its 
outlet,  or  at  its  junction  with  another  tile  drain,  and  proceed  toward  its  upper 
end.     The  ditch  must  be  dug  along  one  side  of  the  line  of  survey  stakes,  and 
about  ten  inches  distant  from  it,  in  a  straight  and  neat  manner,  and  the  top 
soil  thrown  on  one  side  of  the  ditch  and  the  clay  on  the  other.     When  a  change 
in  the  direction  of  ditch  is  made,  it  must  be  kept  near  enough  to  the  stakes  so 
that  they  can  be  used  in  grading  the  bottom.     In  taking  out  the  last  draft,  the 
blade  of  the  spade  must  not  go  deeper  than  the  proposed  grade  line  or  bed  upon 
which  the  tiles  rest. 

3.  Grading  the  Bottom.     The  ditch  must  be  dug  accurately  and  truly 
to  grade  at  the  depths  indicated  by  the  figures  given  by  the  engineer,  measured 
from  the  grade  stakes.     At  each  grade  stake,  a  firm  support  shall  be  erected;  and 
on  these  supports  a  fine,  stout  cord  shall  be  tightly  stretched  over  the  center 
line  of  the  ditch  and  made  parallel  with  the  grade  by  careful  measurements  at 
each  stake,  using  a  carpenter's  level.     Supports  shall  be  kept  erected  at  at  least 
three  grade  stakes,  and  the  work  checked  each  time  by  sighting  over  them. 
Intermediate  supports  shall  be  set  and  lined  in  by  careful  sighting  wherever 
necessary,  to  support  the  cord  every  50  feet.     A  suitable  measuring  stick  shall 
be  passed  along  the  entire  ditch,  and  the  bottom  in  all  parts  made  true  to  grade 
by  measuring  from  the  cord.     The  bottom  must  be  dressed  with  the  tile  hoe,  or, 
in  the  case  of  large  tiles,  with  the  shovel,  so  that  a  groove  will  be  made  to  receive 
the  tile,  in  which  the  tile  will  remain  securely  in  place  when  laid. 

4.  Laying  the  Tile.     The  laying  of  the  tile  must  begin  at  the  lower  end 
and  proceed  upstream.     The  tile  must  be  laid  as  closely  as  practicable,  and 
in  lines  free  from  irregular  crooks,  the  pieces  being  turned  about  until  the  upper 
edge  closes,  unless  there  is  sand  or  fine  silt  which  is  likely  to  run  into  the  tile, 
in  which  case  the  lower  edge  must  be  laid  close,  and  the  upper  side  covered  with 
clay  or  other  suitable  material.   When  in  making  turns,  or  by  reason  of  irregular- 
shaped  tile,  a  crack  of  one-fourth  inch  or  more  is  necessarily  left,  it  must  be 
securely  covered  with  broken  pieces  of  tile.     Junctions  with  branch  lines  must 
be  carefully  and  securely  made. 

5.  Blinding  the  Tile.     After  the  tile  have  been  laid  and  inspected  by 
the  employer  or  his  representative,  they  must  be  covered  with  clay  to  a  depth 
of  six  inches,  unless,  in  the  judgment  of  the  employer  or  his  representative, 
the  tile  are  sufficiently  firm  so  that  complete  filling  of  the  ditch  may  be  made 
directly  upon  the  tile.     In  no  case  must  the  tile  be  covered  with  sand  without 
other  material  being  first  used. 

6.  Risk  During  Construction.     The  ditch  contractor  must  assume  all 
risks  from  storms  and  caving-in  of  ditches;  and  when  each  drain  is  completed, 
it  must  be  free  from  sand  and  mud  before  it  will  be  received  and  paid  for  in  full. 
In  case  it  is  found  impracticable,  by  reason  of  bad  weather  or  unlooked-for 
trouble  in  digging  the  ditch  or  properly   laying  the  tile,  to  complete  the  work 
at  the  time  specified  in  the  contract,  the  time  may  be  extended  as  may  be 
mutually  agreed  upon  by  the  employer  and  contractor.     The  contractor  shall 
use  all  necessary  precaution  to  secure  his  work  from  injury  while  he  is  con- 
structing the  drain. 


86  SEWERS  AND  DRAINS 

7.  The  Tile  to  be  Used.     Tile  will  be  delivered  on  the  ground  convenient 
for  the  use  of  the  contractor.      No  tile  shall  be  laid  which  are  broken,  or  soft, 
or  so  badly  out  of  shape  that  they  cannot  be  well  laid  and  make  a  good,  satis- 
factory drain. 

8.  Prosecution  of  the  Work.     The  work  must  be  pushed  as 'fast  as  will 
be  consistent  with  economy  and  good  workmanship,  and  must  not  be  left  by 
the  contractor  for  the  purpose  of  working  upon  other  contracts,  except  by 
permission  and  consent  of  the  employer.     All  survey  stakes  shall  be  preserved, 
and  every  means  taken  to  do  the  work  in  a  first-class  manner. 

9.  Subletting  Work.     The  contractor  shall  not  sublet  any  part  of  the 
work  in  such  a  way  that  he  will  not  remain  personally  responsible,  nor  shall  any 
other  party  be  recognized  in  the  payment  for  work. 

10.  Plant  and  Tools.     The  contractor  shall  furnish  all  tools  which  are 
necessary  to  be  used  in  digging  the  ditches,  grading  the  bottom,  and  laying 
the  tile.     In  case  it  is  necessary  to  use  curbing  for  the  ditches,  or  outside 
material  for  covering  the  tile  where  sand  or  slush  is  encountered,  the  employer 
shall  furnish  the  same  upon  the  ground  convenient  for  use. 

11.  Payments  for  Work.     Every weeks  during  the  prose- 
cution of  the  work,  the  contractor  may  claim  and  the  employer  shall  pay  75% 
of  the  value  of  the  work  completed  satisfactorily,  the  engineer  being  the  arbiter 
in  case  of  dispute  as  to  the  amount  of  work  satisfactorily  completed.     The 
remaining  25%  will  be  retained  until  the  entire  work  is  completed  satisfactorily, 
as  ^certified  by  the  engineer  after  a  final  inspection,  at  which  time  the  whole 
amount  due  shall  be  paid.     Prior  to  any  payment,  the  employer  may  require  a 
correct  statement  of  all  claims  incurred  by  the  contractor  for  labor,  materials, 
or  damages  on  account  of  the  work ;  and  the  employer  may  withhold  payments 
until  proof  has  been  presented  by  the  contractor  of  release  of  all  liens  against 
the  employer  on  account  of  such  claims. 

12.  Duties  of  Engineer.     The  engineer  shall  have  authority  to  lay  out 
and  direct  the  work,  and  to  inspect  and  supervise  the  same  during  construction 
and  on  completion,  to  see  that  it  is  properly  done  in  accordance  with  the  con- 
tract.    His  instructions  should  be  fully  carried  out. 

13.  Failure  to  Comply  with  Specifications.     In  case  the  contractor  shall 
fail  to  comply  with  the  specifications,  or  refuse  to  correct  faults  in  the  work 
as  soon  as  they  are  pointed  out  by  the  engineer  or  other  person  in  charge,  the 
employer  may  declare  the  contract  void;  and  the  contractor,  upon  receiving 
seventy-five  per  cent  of  the  v(alue  of  the  completed  drains  at  the  price  agreed 
upon,  shall  release  the  work  and  the  employer  may  let  it  to  other  parties. 

71.     Benefits  of  Tile  Drains.    The  advantages  of  tile  drains 
may  be  enumerated  as  follows: 

1.  Tile  drainage,  by  making  the  soil  firm,   enables  earlier 
cultivation  in  the  spring.     Low  ground  drained  can  be  cultivated 
earlier  than  high  ground  not  drained. 

2.  Careful  observations  have  shown  that  tile  drainage  makes 
the  soil  several  degrees  warmer  in  the  spring.     Scientific  tests  have 


SEWERS  AND  DRAINS  87 

shown  this  increased  warmth  to  be  of  the  utmost  importance  in  pro- 
moting the  germination  and  growth  of  crops. 

3.  Tile  drainage  promotes  pulverization  of  the  soil,  putting  it 
in  good  condition  to  cultivate,  and  preventing  baking  and  the  forma- 
tion of  clods. 

4.  Tile  drainage  removes  from  the  pores  of  the  soil  surplus  and 
stagnant  water,  which  would  drown  and  destroy  the  roots  of  plants. 

5.  Tile  drainage  makes  certain  the  proper  "breathing"  of  the 
soil,  or  free  circulation  of  air  in  its  pores,  which  is  essential  to  healthy 
plant  growth. 

6.  Tile  drainage  establishes  in  the  soil  the  proper  conditions 
required  for  the  satisfactory  carrying  on  of  the  chemical  processes 
necessary  to  prepare  the  plant  food  for  its  use  by  vegetation. 

7.  Tile  drainage  fits  the  soil  for  the  vigorous  life  and  action 
of  the  soil  bacteria  which  are  essential  to  preserve  and  increase  its 
fertility  and  promote  the  growth  of  crops. 

8.  Tile  drainage  increases  the  depth  of  soil  which  can  be 
reached  by  the  roots  of  plants  and  drawn  upon  for  plant  food. 

9.  Because  in  them  the  roots  of  plants  can  penetrate  deeper, 
where  they  are  protected  from  heat  and  drouth  and  can  reach  the  deep- 
seated  moisture,  tile-drained  soils  stand  drouth  better  than  undrained 
soils. 

10.  By  putting  the  top  3-feet  or  4-feet  layer  of  soil  into  a  porous 
condition,  tile  drainage  enables  soils  to  absorb  rain  water  instead  of 
discharging  it  over  the  surface,  and  so  helps  to  prevent  surface  wash 
and  consequent  loss  of  fertility. 

11.  By  causing  this  porous  condition,  tile  drainage  makes  the 
upper  3  or  4  feet  of  soil  into  an  enormous  reservoir  to  catch  the  rain 
water  and  discharge  it  only  slowly  into  the  streams.     Thus  tile  drainage 
prevents  floods,  instead  of  causing  them. 

12.  Tile  drainage  does  away  with  irregular  shaped  fields,  cut  up 
by  sloughs  and  ditches,  and  so  cheapens  cultivation. 

Benefits  of  Large  Ditches.  Tile  drainage  is  always  preferred  to 
open-ditch  drainage  if  the  drain  is  not  too  large.  The  advantages  of 
large  ditches  may  be  enumerated  as  follows : 

1.  By  furnishing  channels  to  remove  storm  water,  they  prevent, 
if  of  ample  size,  the  inundation  of  low-lying  lands  by  floods  and  surface 
water. 


88 


SEWERS  AND  DRAINS 


2.  They  have  a  minor  value  for  draining  off  the  ground  water 
from  a  narrow  strip  of  land  each  side. 

3.  One   of   their  main  values  is  in  furnishing  outlets  for  tile 
drains,  and  in  many  places  tile  drainage  is  impracticable  till  outlet 
drainage  ditches  have  been  built. 

72.  Method  of  Computing  Sizes  of  Tile  Drains.  The  drained 
soil  above  the  level  of  tile  drains  contains  a  large  percentage  of  air- 
space in  the  pores  between  the  soil  particles ;  and  this  layer  of  porous 
soil  acts  like  a  great  sponge  several  feet  thick  to  absorb  the  rain  as 
it  falls.  Hence  the  water  reaches  the  tiles  very  slowly.  It  has  been 
found  that  under  average  conditions  tH:s  will  not  be  called  upon  to 
carry  more  than  J-inch  depth  of  water  in  24  hours.  This  equals 
6,800  gallons  per  acre  per  day,  or  4,352,000  gallons  per  square  mile 
per  day.  The  sizes  of  tile  drains  for  average  conditions  may  readily 
be  taken  from  Table  IX. 

TABLE  IX 

Number  of  Acres  Drained  by  Tiles  Removing  J^-Inch  Depth  of  Water 

in  24  Hours 


GRADES 

DIAMETERS  OF  TILE  DRAINS 

Per 
cent 

Inches 
per  rod 

3 
in. 

4 
in. 

6 
in. 

8 
in. 

10 
in. 

12 
in. 

15 
in. 

18 
in. 

20 
in. 

22 
in. 

24 

in. 

0.03 

TV 

37 

59 

109 

159 

205 

254 

319 

0.05 

5 

13 

28 

49 

75 

131 

219 

264 

332 

411 

0.10 

V 

4 

7 

19 

40 

69 

109 

186 

289 

373 

471 

582 

0.15 

A 

4 

9 

24 

49 

85 

132 

232 

355 

458 

577 

713 

0.25 

% 

5 

10 

28 

56 

97 

153 

264 

410 

529 

667 

823 

0.30 

& 

6 

12 

33 

69 

119 

188 

322 

502 

648 

808 

1,008 

0.40 

it 

7 

14 

39 

79 

138 

216 

371 

580 

748 

942 

1,165 

0.50 

8 

16 

44 

89 

154 

246 

416 

648 

838 

1,050 

1,300 

0.60 

1A 

9 

17 

48 

97 

169 

266 

457 

710 

911 

1,154 

1,422 

0.70 

m 

10 

19 

50 

105 

182 

287 

488 

768 

988 

1,242 

1,549 

0.80 

IT'S 

10 

20 

55 

114 

195 

307 

526 

822 

1,059 

1,332 

1,645 

0.90 

ill 

10 

21 

59 

119 

207 

326 

558 

872 

1,123 

1,414 

1,747 

1.00 

2 

11 

22 

62 

126 

218 

343 

589 

917 

1,176 

1,495 

1,838 

1.50 

3 

13 

28 

75 

153 

267 

419 

722 

1,123 

1,450 

1,824 

2,256 

2.00 

4 

15 

31 

88 

178 

309 

485 

832 

1,297 

1,676 

2,110 

2,594 

3.00 

5}| 

19 

39 

107 

216 

377 

593 

1,020 

1,589 

1,957 

2,592 

4.00 

7|| 

22 

45 

123 

253 

437 

683 

1,176 

5.00 

9% 

25 

50 

138 

280 

486 

765 

7.50 

14% 

30 

61 

169 

34* 

10.00 

19H 

35 

71 

195 

Table  IX  is  computed  from  the  form  of  Poncelet's  formula  recommended 
for  use  with  tile  drains  by  C.  G.  Elliott,  drainage  expert  to  the  U.  S.  Agricultural 
Department,  Washington,  D.  C.,  who  recommends  the  above  sizes  to  drain 


SEWERS  AND  DRAINS  89 

ground  water  only.  If  surface  water  is  also  to  be  removed,  as  in  the  case  of 
ponds  without  other  outlets,  the  tiles  will  drain  safely  only  one-half  to  one- 
third  the  number  of  acres  given  in  the  table. 

When  part  of  the  land  in  the  watershed  is  rolling,  not  requiring  tiling, 
count  only  one-fifth  to  one-third  of  such  rolling  land,  in  addition  to  all  of  the 
low,  flat  land,  in  getting  the  size  of  tiles  to  remove  ground  water  only. 

Example  41.  What  size  of  tile  laid  to  a  0.1  per  cent  grade  will  carry 
the  under-drainage  of  160  acres  of  flat  land? 

Answer.     15  inches. 

Example  42.  What  size  of  tile  to  a  0.2  per  cent  grade  will  carry 
the  under  drainage  of  240  acres,  two-thirds  rolling  ? 

Answer.  80  acres  flat  land,  plus  one-third  of  160  acres  rolling,  gives 
133J  acres,  requiring  a  12-inch  tile. 

Example  43.  What  size  of  tile  laid  to  0.3  per  cent  grade  will  be 
required  to  remove  both  ground  and  surface  water  from  a  pond  whose 
watershed  includes  40  acres? 

Answer.  10-inch.  (NoTE. — Double  or  triple  the  area  for  both 
ground  and  surface  water.) 

73.  Method  of  Computing  Sizes  of  Drainage  Ditches.    Since 
drainage  ditches  must  carry  surface  water  as  well  as  ground  water, 
their  capacities  must  be  larger  than  those  of  tile  drains  for  the  same 
number  of  acres  drained.     It  has  been  found  by  experience  that  they 
must  carry  from  f -inch  depth  for  small  drainage  areas,  to  J-inch  depth 
for  large  drainage  areas  per  day.  Their  size  can  be  taken  from  Table  X. 

Example  44.  What  width  of  ditch,  having  a  fall  of  5  feet  per  mile, 
and  a  depth  of  water  of  3  feet,  will  be  required  to  drain  an  area  of  5  square 
miles  (3,200  acres)  ? 

Answer.     About  12  feet. 

Example  45.  What  size  ditch  having  a  fall  of  3  ft.  per  mile,  and 
9  ft.  depth  of  water,  will  drain  an  area  of  three  townships  (69,120  acres)  ? 

Answer.     About  22  feet. 

74.  Method  of  Computing  Sizes  of    Subdrains    for    Sewers. 
Sewer  subdrains  act  like  tile  land  drains  to  remove  the  ground  water 
from  the  soil.     Being  deeper,  they  will  drain  wider  strips  of  land — 
say.  averaging  16  rods  wide,  instead  of   8  rods,  for   ordinary  land 
drains  in  average  soil ;  but  also,  owing  to  the  greater  depth,  the  water 
will  reach  the  tiles  more  slowly,  and  this  may  offset  the  greater  width 
drained.     We  may  assume  roughly  that  each  subdrain  may  be  called 
upon  to  remove  J-inch  depth  of  water  per  day  from  a  strip  16  rods 
wide,  which  is  the  same  thing  as  ^-inch  depth  per  day  from  a  strip  of 
land  8  rods  wide. 


90 


SEWERS  AND  DRAINS 


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92 


SEWERS  AND  DRAINS 


Hence  the  sizes  required  for  sewer  sub-drains  may  be  taken  from 
Table  IX,  calculating  the  number  of  acres  drained  by  multiplying  the 
total  lengths  of  tributary  drain  tile,  in  feet,  by  132  feet  (  =  8  rods),  and 
dividing  the  product  by  43,560  sq.  ft. 

The  above  method  will  give  a  capacity  approximating  110,000 
gallons  per  day  per  mile  of  tributary  subdrains.  As  sewers  are 
ordinarily  distributed,  it  will  give  a  capacity  approximating  1,500,000 
gallons  per  day  per  square  mile  of  territory  served  by  the  sewers. 

Example  46.  Calculate  the  size  of  subdrains  laid  to  a  0.25 
per  cent  grade,  required  to  serve  as  outlet  for  30,000  linear  feet  of 
tributary  subdrains. 

Solution:    30,000  X  132 

.o  rfiQ —  -  =  91  acres  =  eauivalent  area  drained 

for  J-inch  depth. 

In  Table  IX,  opposite  the  0.25  per  cent  grade,  we  find  that  a  10- 
inch  tile  would  be  required. 

Answer.     10-inch  tile  subdrain. 

75.  Cost  of  Tile  Land  Drains  and  Drainage  Ditches.  The 
cost  of  tile-drain  construction  in  central  Iowa  in  1904,  can  be  approxi- 
mated from  Table  XL  Local  prices  should  be  determined  before 
using  the  table  for  close  estimates  of  work  done  elsewhere. 

TABLE  XI 
Cost  of  Tile  Drains 


COST  op  DIGGING  AND  LAYING, 

PER  ROD 

SIZE  OF 
TILE 

PRICE    PER 
1,000  FEET 

WEIGHT 
PER  FOOT 

COST  OF 
HAULING 
1,000  FEET 
5  MILES 

3  feet  deep 

Add  per  foot  for  addi- 
tional depth  over  3 
feet 

REFILLING, 
PER  ROD 

or  less 

3-6  ft. 

over  6  ft. 

3  in. 

$   16.00 

5 

$  3.12 

$  0.35 

$  0.15 

$  0.30 

2c.-5c. 

4  in. 

22.00 

8 

5.00 

0.35 

0.15 

0.30 

2c.-5c 

Sin. 

30.00 

10 

6.25 

0.35 

0.15 

0.30 

2c.-5c. 

Gin. 

40.00 

12 

7.50 

0.35 

0.15 

0.30 

2c.-5c. 

Tin. 

50.00 

15 

9.37 

0.35 

0.20 

0.35 

2c.-5c. 

Sin. 

60.00 

20 

12.50 

0.40 

0.20 

0.35 

2c.-5c. 

10  in. 

95.00 

30 

18.75 

0.45 

0.20 

0.35 

2c.-5c. 

12  in. 

120.00 

40 

25.00 

0.50 

0.20 

0.35 

2c.-5c. 

15  in. 

250.00 

50 

31.25 

18  in. 

400.00 

80 

50.00 

20  in. 

600.00 

100 

62.50 

24  in. 

800.00 

125 

78.12 

SEWERS  AND  DRAINS  93 

The  cost  of  hauling  given  in  Table  XI  is  on  the  basis  of  $1 .25  per  ton,  or 
$2.50  per  day  for  a  man  and  team,  making  two  trips. 

The  prices  for  digging  and  laying  given  above  include  board  furnished  by 
the  ditcher.  If  the  farmer  furnishes  board,  deduct  about  20  per  cent.  The 
prices  for  digging  and  laying  are  for  average  ground,  and  should  be  increased 
for  quicksand  or  very  wet  soils. 

N.  B.  To  all  estimates  it  is  wise  to  add  5  per  cent  to  10  per  cent  for  con- 
tingencies and  engineering. 

Example  47.  What  will  be  the  cost  of  2,000  feet  of  6-in.  tile  drain, 
2J  miles  from  the  tile  yard,  of  which  1,000  feet  is  4  feet  deep,  500  feet  5 
feet  deep,  and  500  feet  6  feet  deep,  in  average  soil  ? 

Answer: 

2,000 ft.  of  6  in.  tile  @  $40.00 $80 

Hauling  2,000  ft.  1\  miles,  @  $3 .75.. . . 7£ 

Digging  and  laying  60'.  6  rods  4  ft.  deep,  @  50c 30£ 

"    30. 3 rods  5 ft.  deep,  @  65c 19* 

"         "    30. 3  rods  6 ft.  deep,  @80c 24 

Refilling  121 .2  rods  (by  team),  @  2c 2£ 

$164 

Add  10  per  cent  for  engineering,  etc 16 

Estimated  cost $180 

Cost  of  Open  Drainage  Ditches.  The  cost  of  open  drainage  ditches 
is  estimated  by  the  cubic  yard. 

To  calculate  the  number  of  cubic  yards  per  foot  of  length  of  ditch, 
multiply  the  average  width  by  the  average  depth,  and  divide  by  27.  Thus 

7  X  12 
a  7-ft.  by  12-ft.  ditch  contains — ==—  =  3^  cubic  yds.  per  foot  length. 

27 

The  cost  per  cubic  yard  in  Iowa  varies  from  7c.  to  18c.,  depending 
on  the  size  of  the  job,  the  character  of  the  soil,  and  other  local  conditions, 
including  the  certainty  of  the  contractor  getting  his  money  promptly.  The 
larger  the  work,  the  less  is  the  cost  per  cubic  yard. 

HOUSE  SEWERAGE 

76.  Definitions  and  General  Description.  A  house  sewer  is  a 
small  branch  sewer  which  connects  the  house  with  the  street  sewer. 
In  Fig.  6  a  general  view  of  a  house  sewer  is  given. 

A  soil  pipe  is  the  main  drainage  pipe  of  the  system  of  house 
plumbing,  into  which  the  different  fixtures  discharge.  See  Fig.  35. 

A  trap  is  a  bend  or  depression  in  a  pipe  or  drain,  which  remains 
constantly  full  of  liquid,  thus  shutting  off  air-connection  between  the 
portions  of  the  pipe  or  drain  on  opposite  sides  of  the  trap.  See  Fig.  35. 

A  general  idea  of  an  entire  system  of  house  sewerage  can  be 
obtained  from  Figs.  6  and  35,  which  s«e. 


94 


SEWERS  AND  DRAINS 


The  house  sewer  and  outlet  for  the  cellar  and  foundation  drains, 
extend  from  the  street  sewer  to  the  house  as  shown  in  Fig.  6. 

The  iron  soil  pipe  should  begin  a  few  feet  outside  the  house,  and 
extend  full  size  through  the  roof,  the  separate  fixtures  discharging 
into  the  soil  pipe,  each  protected  by  a  trap,  and  all  traps  being  vented, 
as  shown  in  Fig.  35.  The  dotted  lines  in  Fig.  35  show  alternative 

plans    sometimes     adopted 
for  house  sewerage. 

77.    House   Sewers. 
House  sewers  (see  Fig.  6) 
are  usually  made  of  vitrified 
sewer    pipe    the    same    as 
street  sewers,  and  should  be 
constructed   with    fully    as 
much    care.     The    joints 
should  have  gaskets  of  hemp 
QJ  or  oakum,  and  be  carefully 
j£  cemented,  the  same  as  street 

^  sewers.     (See  Art.  33.) 
1  o 
u*      Each  piece  of  pipe  should 

.£  be  laid  to  the  exact  grade  by 
measuring  from  a  grade 
string,  the  same  as  for  street 
sewers  (see  Art.  98).  The 
grade  should  usually  be  not 
less  than  2  per  cent.  The 
house  sewer  should,  if  possi- 
ble, be  perfectly  straight,both 
in  alignment  and  in  grade, 
from  the  house  to  the  house 
connection  at  the  sewer. 

Fig.  35.    Diagram  of  House  Sewerage  System.  Inspection     pipes     should 

be  placed  just  inside  the  lot  line,  as  indicated  in  Fig.  6. 

House  sewers  should  usually  be  4-inch  circular  pipe.  If 
too  large,  they  are  more  difficult  to  keep  flushed  clean,  and  they  may 
carry  to  the  street  sewer  things  large  enough  to  cause  stoppages, 
improperly  put  into  the  house  fixtures.  Sometimes  5-inch  or  6-inch 
house  sewers  are  used. 


SEWERS  AND  DRAINS  95 

78.  General  Principles    of    House    Plumbing.    The  following 
general  principles  should  be  carefully  observed  in  the  installation  of 
all  house  plumbing: 

1.  The  iron  pipe  should  begin  a  few  feet  outside  the  house, 
as  vitrified  pipe  does  not  have  tight  joints  and  is  liable  to  be  broken, 
where  it  passes  through  the  foundation  wall,  by  uneven  settlement. 

2.  No  pipes  carrying  sewage  should  be  allowed  to  be  buried 
under  the  basement  floor,  unless  placed  in  masonry-lined  trenches 
with  removable  covers. 

3.  All  pipes  of  the  plumbing  system  should  be  iron  or  lead, 
with  absolutely  tight  joints  of  lead,  or  screwed,  or  soldered. 

4.  In  general,  no  pipes  should  be  built  into  partitions  or  walls, 
where  they  cannot  be  gotten  at,  unless  removable  panels  are  placed 
over  them. 

5.  All  fixtures  should  be  completely  exposed  to  view,  and 
should  not  be  enclosed  in  woodwork.     Sinks  and  washbowls,  for 
example,  should  be  supported  on  brackets  or  legs,  with  clear,  open 
spaces  under  them. 

6.  All  fixtures  should  be  of  durable,  smooth,  and  non-ab- 
sorbent material,  such  as  porcelain  or  enameled  iron.     The  least 
possible  woodwork  should  be  used. 

7.  All  fixtures  should  be  located  in  well-lighted  and  well- 
ventilated  places. 

8.  Each  fixture  must  be  protected  by  a  good  trap.     There 
must  be  no  openings  from  the  plumbing  system  into  the  interior  of 
the  house  not  thoroughly  protected  by  traps  sure  to  stav  full  of  liquid. 

9.  Thorough  ventilation  of  all  pipes  must  be  provided  for. 

10.  All  pipes  must  be  laid  to  good  grades,  without  sags,  so  as 
to  drain  completely  and  quickly. 

11.  The  cellar  and  foundation  drains  should  be  connected  with  a 
sewer  subdrain,  if  possible,  and  not  with  a  sewer,  owing  to  the  danger 
of  the  water  in  the  traps  evaporating  in  dry  weather  when  no  water 
runs  in  the  drains.     If  absolutely  necessary  to  connect  to  the  sewer,  ex- 
cessively deep  traps  should  be  used,  to  lessen  the  danger  of  evaporation, 

79.  Soil  Pipes.    The  iron  soil  pipe  begins,  as  already  stated, 
a  few  feet  outside  the  foundation  wall.     At  this  point  a  disconnecting 
trap  is  sometimes  placed,  as  shown  by  the  dotted  lines  in  Fig.  35, 
in  which  case  a  fresh-air  inlet  must  be  placed  on  the  house  side  of  the 


9G  SEWERS  AND  DRAINS 

trap,  as  also  shown  by  dotted  lines  in  Fig.  35,  to  permit  complete 
ventilation  of  the  soil  pipe. 

The  soil  pipe  should  extend  full-sized  and  without  any  obstruc- 
tion, a  few  feet  above  the  roof.  It  should  everywhere  be  readily 
accessible,  and  will  naturally  be  placed  in  the  location  most  convenient 
for  attaching  the  fixtures. 

The  soil  pipe  is  usually  4  inches  in  diameter,  made  of  cast  iron, 
with  air-tight,  leaded  and  calked  joints. 

80.  Traps.    The  best  traps  are  simply  smooth  bends  in  the 
plumbing  pipes,  giving  depressions  which  stand  full  of  liquid.     If 
the  curves  are  not  smooth,  or  if  there  are  sudden  changes  in  size,  the 
danger  of  stoppage  is  increased.     The  depth  from  the  highest  level 
of  the  water  in  the  trap  to  the  top  of  the  liquid  in  the  lowest  portion, 
is  called  the  seal  of  the  trap.     Traps  are  necessary  evils  in  plumbing 
systems,  as  they  tend  to  cause  stoppages. 

The  seals  of  traps  may  be  forced  by  any  compression  or  rare- 
faction of  air  in  the  plumbing  pipes,  such  as  may  be  caused  by  plugs 
of  sewage  from  other  fixtures  descending  the  pipes,  unless  a  vent  pipe  is 
extended  from  the  crown  or  highest  point  of  each  trap  on  the  side  next 
to  the  soil  pipe,  as  shown  in  Fig.  35. 

Traps  should  be  located  as  closely  as  possible  to  the  fixtures  they 
are  to  protect. 

81.  Ventilation.    The  vent  pipes  from  the  traps  mentioned  in 
Art.  80,  above,  and  shown  in  Fig.  35,  serve  also  to  secure  ventila- 
tion of  branch  pipes.    They  should  unite  in  a  main  vent  pipe,  2  inches 
in  diameter,  as  shown  in  Fig.  35,  and  this  may  turn  into  the  soil  pipe 
above  the  highest  fixture,  or  may  extend  independently  above  the 
roof,  as  shown  by  the  dotted  lines  in  Fig.  35. 

The  extension  of  the  main  soil  pipe  unobstructed  through  the 
roof,  with  admission  of  air  from  the  sewer  (or  through  the  fresh-air 
inlet  if  a  disconnecting  trap  is  used),  together  with  the  trap  vent 
pipes  and  the  main  vent  pipe,  as  shown  in  Fig.  35,  insure  ventilation 
of  all  parts  of  the  plumbing  system. 

COST  OF  SEWERS,  AND  METHODS  OF  PAYING 
FOR  THEM 

82.  Preliminary  Estimates  of  Cost  of  Sewers.    One  of  the  first 
things  which  the  sewerage  engineer  will  be  asked  about  sewers  for 


SEWERS  AND  DRAINS  97 

which  he  has  made  plans,  is  what  will  be  their  cost.  He  must  be 
able  to  answer  this  question  readily,  and  with  close  approximation  to 
the  actual  cost. 

Many  factors  affect  the  cost  of  sewers,  some  of  which  cannot  be 
exactly  foretold.  Among  the  things  which  can  be  closely  ascertained 
in  advance,  are  the  sizes,  lengths,  and  depths  of  the  sewer,  and  the 
amounts  of  the  various  kinds  of  materials  required.  Among  the 
things  which  cannot  be  exactly  foretold,  are  the  nature  of  the  soil,  the 
amount  of  ground  water  to  be  encountered,  the  weather  conditions, 
and  the  labor  conditions. 

The  competent  engineer  will  thoroughly  study  all  conditions 
which  may  affect  the  cost,  before  preparing  his  estimates,  and  even 
then  will  allow  a  liberal  percentage  for  contingencies. 

The  engineer  should  have  borings  made  to  determine  the  char- 
acter of  the  soil  and  the  level  of  ground  water,  and  should  learn  all 
he  can  of  previous  experience  in  the  town  with  ditches  and  other 
excavations.  Even  then  the  actual  soil  often  proves  very  different 
from  what  was  anticipated. 

After  making  the  preliminary  study  and  plans,  the  engineer 
tabulates  the  sewers  by  lengths,  depths,  sizes,  and  character,  together 
with  the  manholes,  lampholes,  flush-tanks,  and  other  items  of  the 
system.  He  then  assigns  a  unit  price  to  each  item,  after  careful 
study  of  all  conditions,  and  calculates  the  total  cost. 

The  data  of  cost  which  follow  are  for  average  conditions  only, 
and  only  for  the  localities  named.  They  will  need  to  be  modified 
by  the  engineer  to  meet  different  conditions. 

83.  Cost  of  Pipe  Sewers.  In  estimates  of  the  cost  of  pipe 
sewers,  the  work  is  usually  divided  into  the  following  items: 

(1)  Trenching  and  Refilling.  This  includes  excavating  the 
trench  for  the  sewer,  refilling  it,  and  compacting  the  material  after 
the  sewer  pipe  is  laid.  Trenching  and  refilling  are  usually  itemized 
according  to  depth,  thus : 

Trenching  and  Refilling  under  6  feet  depth 

"       6  to  8  feet  depth 

8  to  10  feet  depth 
Etc.,  etc. 

The  cost  of  trenching  and  refilling  will  vary  somewhat  also  with 
the  diameter  of  the  sewer;  but  this  is  often  not  separately  itemized. 


98  SEWERS  AND  DRAINS 

For  estimates  and  bids,  the  lengths  in  linear  feet  of  each  depth  of 
sewer  are  taken  from  the  profiles,  and  listed  in  the  tabulation. 

(2)  Furnishing    Sewer    Pipe    and    Specials.    The    pipe    are 
usually  specified  to  be  delivered  on  board  cars  at  the  town  where  they 
are  to  be  used.     The  amounts  are  usually  itemized  according  to  the 
diameters,  thus: 

Furnishing  sewer  pipe    8  inches  diameter 
»               »             "10  "  " 

»>  »  »      ^2  "  " 

etc.,  etc. 

Specials  are  sometimes  itemized  separately,  and  sometimes 
included  in  the  prices  for  furnishing  pipe,  the  average  distance  apart 
being  specified. 

For  estimates  and  bids,  the  total  lengths  of  each  size  of  pipe  are 
ascertained  and  listed  in  the  tabulation. 

(3)  Hauling   and  Laying   Sewer  Pipe    and   Specials.    This 
includes  taking  the  sewer  pipe  from  the  cars,  hauling  them  to  the 
sewer,  furnishing  cement,  sand,  and  hemp  or  oakum,  and  laying  the 
pipe  according  to  the  specifications.     Some  labor  in  excavating  bell 
holes  and  a  few  inches  at  the  bottom  of  the  ditch  shaped  to  fit  closely 
the  under  side  of  the  pipe,  is  also  included.     Hauling  and  laying  are 
usually  itemized  according  to  the  diameters  of  the  pipe,  thus : 

Hauling  and  Laying  sewer  pipe  and  specials,    8  inches  diameter 

>y  »  »  »  »  ;?  j»  i  n         »  » 

»  )>  )j  »  »  »  »  -10         »  )> 

Etc.,  etc. 

The  lengths  of  each  size  are  listed  for  estimates  and  bids,  the 
same  as  sewer  pipe. 

In  Fig.  36  is  given  a  diagram  for  estimating  the  cost  of  pipe 
sewers  and  subdrains  in  the  Middle  West.  It  may  be  used  elsewhere 
by  noting  local  conditions  and  their  variation  from  the  conditions 
assumed,  as  follows: 

(a)  If  the  sewers  are  to  be  paid  for  promptly  as  the  work  pro- 
gresses, in  cash  instead  of  in  assessment  certificates,  deduct  about 
10  per  cent. 

(b)  Get  actual  prices  on  sewer  pipe  delivered,  and  add  about 
8  per  cent  for  additional  cost  of  specials  in  the  average  residence 
district,  and  16  per  cent  in  the  average  business  district. 


SEWERS  AND  DRAINS  99 

(c)  Ascertain  the  character  of  the  soil,  and  the  likelihood  of 
encountering  ground  water.  If  the  conditions  are  very  favorable, 
the  cost  of  trenching,  refilling,  and  pipe  laying  may  be  materially 
decreased,  even  sometimes  to  50  per  cent  of  the  figures  shown  in  the 
diagram;  while  on  the  other  hand,  for  very  unfavorable  conditions, 
the  cost  shown  for  these  items  will  have  to  be  increased,  sometimes 
even  to  150  per  cent. 

Example  48.  Estimate  the  cost  of  a  pipe  sewer  consisting  of 
1,200  ft.  of  18-inch  pipe  averaging  16  feet  deep,  and  2,700  feet  of 
15-inch  pipe  averaging  12  ft.  deep,  under  average  conditions,  together 
with  a  6-inch  subdrain. 

Solution : 

1,200  X  2.35  (from  diagram)  =  $3,020  for  18-inch  sewer 

2,700  XL  60  (  "          "       )  =     4,320  "    15     " 

3,900  XO.  15  ("  "       )  = 585"      6     "     subdrain 

Answer.  Total  estimated  cost  =  $7,925 

84.  Cost  of  Brick  Sewers.  The  cost  of  a  brick  sewer  may  be 
estimated  by  determining  separately  the  cost  of  the  excavation  and 
refilling  and  that  of  the  brickwork.  The  number  of  cubic  yards  of 
each  of  these  items  is  computed  for  1  linear  foot  length  of  sewer;  and 
the  cost  per  linear  foot  is  estimated  by  multiplying  the  results  so 
obtained  by  estimated  costs  per  cubic  yard  of  excavation  and  brickwork 
respectively. 

(1)  To  calculate  the  number  of  cubic  yards  of  excavation  per 
linear  foot  length  of  sewer,  multiply  the  average  depth  of  sewer  trench 
by  the  average  width,  and  divide  by  27. 

The  average  depth  for  a  circular  bottom  will  approximate  the 
average  depth  from  the  surface  to  the  invert,  while  the  average  width 
will  be  at  least  as  great  as  the  internal  diameter  plus  twice  the  thickness 
of  the  brickwork. 

Thus,  for  a  2-ring  (9  inches  of  brickwork)  circular  sewtr  6  feet  in 
diameter,  with  grade  line  12  ft.  deep,  the  number  of  cubic  yards 
excavation  per  linear  foot  of  sewer  is : 

12X(6  +  1J)       90 
27 —       =  27~  ^    ^  CU'  y       per  lmear  ft- 

The  cost  of  sewer  excavation  and  refilling  varies  usually  from 
$0.20  per  cu.  yd.  to  $1.20  per  cu.  yd.,  averaging  perhaps  $0.50  to 
$0.75  per  cu.  yd. 


100 


SEWERS  AND  DRAINS 


SEWERS  AND 


101 


Thus,  for  average  conditions,  fairly  favorable',  the  cost  of  exca- 
vation for  the  6-foot  sewer,  12  feet  deep,  referred  to  above,  would  be 
31  x  .60  =  $2.00  per  linear  foot. 

The  favorable  conditions  for  low  cost  per  cubic  yard,  are,  large 
sewers;  neither  great  shallowness  nor  excessive  depth;  little  water; 
soil  firm  enough  not  to  require  much  bracing,  yet  not  hard  enough 
to  require  to  be  picked;  and  the  use  of  excavating  machinery.  The 
opposites  of  these  conditions  give  the  unfavorable  conditions. 

(2)  The  number  of  cubic  yards  of  brickwork  pvr  linear  foot  of 
brick  sewers,  may  be  taken  from  Tables  XII  and  XIII,  which  are 
taken  mainly  from  Gillette's  Handbook  of  Cost  Data. 

TABLE  XII 
Cubic  Yards   per  Linear    Foot   of   Brick    Masonry   in   Circular  Sewers 


DIAMETER 

ONE  RING 

Two  RINGS 

THREE  RINGS 

2ft.  6  in. 

0.125 

0.283 

3 

0 

0.147 

0.327 

3 

6 

0.169 

0.371 

4 

0' 

0.191 

0.415 

4 

6 

0.213 

0.418 

5 

0 

0.234 

0.502 

0.802 

5 

6 

0.256 

0.544 

0.867 

6 

0 

0.278 

0.589 

0.933 

6 

6 

0.633 

0.998 

7 

0 

0.677 

0.063 

7 

6 

0.720 

0.128 

8 

0 

0.764 

1.194 

8 

6 

0.807 

1.260 

9 

0 

0.851 

1.325 

9 

6 

0.895 

1.390 

10 

0 

0.938 

1.456 

TABLE  XIII 
Cubic  Yards  per  Linear  Foot  of  Brick  Masonry  in  Egg-Shaped  Sewers 


DIMENSIONS 

ONE    RING 

Two  RINGS 

THREE  RINGS 

ft.  in.         ft.  in. 

2-0     by    3-6 

0.128 

0.286 

2-6       '      3-9 

0.154 

0.341 

3-0            4-6 

0.182 

0.396 

3-6             5-3 

0.451 

0.725 

4-0             6-0 

0.506 

0.808 

4-6             6-9 

0.561 

0.891 

5-0            7-6 

0.617 

0.974 

5-6             8-3 

0.673 

1.056 

6-0            9-0 

0.729 

1.140 

6-6             9-9 

0.785 

1.223 

102  SEWERS  AND  DRAINS 

The  cost  of  brick  masonry  in  sewers  usually  varies  from  $8 . 00  to 
$14.00  per  cubic  yard,  averaging  perhaps  $9.50  to  $12.00. 

Thus,  under  average  conditions,  the  cost,  per  linear  foot,  of  the 
brick  masonry  of  the  two-ring,  6-foot  circular  brick  sewer  mentioned 
above,  would  be  about  0.589  cu.  yds.  (from  Table  XII)  X  $10.50  per 
cu.  yd.  =  $6.17  per  foot.  It  will  depend  upon  the  grade  of  brick 
used,  their  cost  per  1,000,  the  cost  and  proportions  of  cement  and 
sand  in  the  mortar,  the  wages  of  brick  masons,  the  size  and  depth  of 
the  ditch,  etc. 

Example  49.  Estimate  the  cost,  under  fairly  favorable  condi- 
tions, as  to  excavation  and  brickwork,  of  a  10-foot,  3-ring,  circular 
brick  sewer  1,875  ft.  long,  averaging  10  ft.  deep. 

Solution : 

10  X  13 
.  Cu.  yds.  excavation   per  foot  =  about      — ^= —      =  5 

(allowing  13  ft.  width  of  trench,  to  provide  a  little  extra  room  for 
bracing). 

Since  the  conditions  are  fair,  assume  $0.60  per  cu.  yd.  as  cost 
of  excavation  and  refilling. 

The  brickwork  =  1.456  cu.  yds.  per  linear  foot  (Table  XII);  and 
since  the  conditions  are  fair,  we  shall  assume  a  cost  of  $9.50  per  cu.  yd. 

Then  the  estimate  will  be  as  follows: 

Excavation  and  Refilling,         5  X  $0 . 60  =  $  3 . 00  per  lin.  ft. 

Brickwork  1 .456  X    9.50=     13.83"     "     " 

Total  $16.83"     "     " 

1,875  X  16.83  ==  $31,556  for  total  cost,  to  which,  however,  it 
may  be  wise  to  add,  say,  5  to  10  per  cent  for  contingencies  unforeseen. 

Answer.     About  $33,500. 

85.  Cost  of  Concrete  Sewers.  The  cost  of  concrete  sewers 
may  be  estimated  by  a  method  precisely  similar  to  that  described  in 
Art.  84,  above,  for  brick  sewers — namely: 

(1)  Compute  the  cubic  yards  of  excavation  per  linear  foot  of  sewer 
l_  average  depth  X  average  width)^  andmultiply  by  the  esfimafed 

cost  per   cubic  yard,  which  will  be   from  $0.20    to    $1.20,  usually 
$0.50  to  $0.75. 


SEWERS  AND  DRAINS  103 

(2)     Compute  the  number  of   cubic  yards  of    concrete  per  linear 
foot  of  sewer 

total  area  of  concrete  in  square  feet  in  a  cross-section  of  the  sewer 


(tot 


and  multiply  by  the  estimated  cost  of  the  concrete  per  cubic  yard,  which 
will  be  from  $6.50  to  $12.00,  usually  from  $7.50  to  $9.50. 

(3)  In  the  case  of  reinforced  concrete  sewers,  compute  the  number 
of  pounds  of  steel  reinforcing  per  linear  foot  of  sewer,  and  multiply  by 
$0.04  to  $0.05  per  Ib. 

The  details  of  designs  for  concrete  and  reinforced  concrete 
sewers  vary  so  much  that  no  tables  can  be  given,  as  for  brick  sewers, 
showing  the  cubic  yards  of  concrete  per  linear  foot  of  sewer. 

The  cost  of  the  concrete  will  depend  upon  the  costs  of  cement, 
sand,  and  broken  stone  or  gravel,  and  on  their  proportions;  on  the 
size  and  depth  of  the  trench  and  its  freedom  from  water;  on  the 
cost  of  labor,  etc. 

86.  Cost  of  Manholes,  Combined  Manholes  and  Flush=Tanks, 
Flush=Tanks,  Lampholes,  and  Deep=Cut  House  Connections.    Under 
these  headings  the  following  data  of  cost  will  be  found  valuable  : 

Manholes.  Under  average  conditions,  the  cost  of  brick  man- 
holes of  the  design  shown  in  Fig.  9,  will  be  about  $40  for  8  ft.  depth 
of  sewer.  For  greater  depths,  add  about  $3  per  foot  of  additional 
depth. 

Combined  Manholes  and  Flush-Tanks.  Under  average  con- 
ditions, the  cost  of  these  may  be  estimated  at  $80,  plus  $4  per  foot 
of  additional  depth  of  sewer  over  8  ft.  This  is  for  about  500  gallons' 
capacity  of  the  flush-tank  part. 

Flush-tanks  of  500  gallons'  capacity,  under  average  conditions, 
may  be  estimated  to  cost  about  $60  each. 

Lampholes,  such  as  shown  in  Fig.  10,  may  be  estimated  at  about 
$10,  plus  $0  .  35  per  foot  of  additional  depth  over.  8  feet. 

Deep-cut  house  connections  (see  Fig.  8)  may  be  estimated  at 
$2.00  to  $3.00  each,  according  to  the  depth  of  the  sewer. 

87.  Engineering  and  Contingencies.     In  estimates  of  the  cost 
of  a  sewer  system,  it  is  necessary  to  allow  for  unforeseen  contingencies 
and  for  the  cost  of  the  engineering  work.     From  5  per  cent  to  20  per 
cent  is  usually  added  to  the  estimated  cost  on  these  accounts,  depend- 


104 


SEWERS  AND  DRAINS 


ing  upon  the  certainty  or  uncertainty  of  the  knowledge  of  all  the 
conditions. 

EXAMPLE  FOR  PRACTICE 

88.  Example  50.  Estimate  the  cost  of  the  sewer  system  shown 
below,  the  conditions  being  assumed  to  be  average.  (NOTE:  See 
Articles  84  to  87,  inclusive.) 

PRELIMINARY  ESTIMATE  OF  COST  OF  SEWER  SYSTEM  FOR 


COST 

ITEM 

APPROX. 

Q.UANTITY 

Unit 

Total 

4-ft.  brick  sewer  ,    2  rings,     8  ft.  average  depth 

850  ft. 

3-ft.      "                   2             10  " 

625     ' 

24-in.  pipe  sewer,      9  ft.  average  depth 

18    "       "           "     11 

3,780     ' 
1,740 

12    "       "           "     14 

2,640     ' 

8    "       "           "     10J 

46,800     ' 

Manholes                  12 

68 

Comb.M.H.&F.T.lO 

18 

Lampholes               1  1 

38 

Total  of  above 

Engineering  and  Contingencies,  10  per  cent  of  above, 

Total  estimate  of  cost 

* 

*  Answer.    About  $82, 500. 

89.  Methods  of  Paying  for  Sewers.  This  is  another  question 
which  comes  up  early  in  determining  whether  a  city  can  or  will  build 
or  extend  a  sewer  system. 

Three  methods  are  in  common  use  in  paying  for  sewers,  as 
follows : 

(1)  The  City  as  a  whole  may  pay  the  entire  cost.  When  this 
plan  is  followed,  all  or  part  of  the  money  may  be  raised  by  selling 
bonds,  or  all  or  any  part  may  be  raised  at  once  by  taxation. 

In  some  States,  cities  are  given  a  right  to  levy  a  sewer  tax  of  a 
certain  rate  for  a  certain  number  of  years  in  advance,  and  to  anticipate 
the  proceeds  of  this  tax  by  issuing  sewer  warrants. 

Often,  when  it  comes  to  the  construction  of  sewers,  the  City  will 
be  found  to  have  already  issued  bonds  to  the  highest  legal  amount, 
to  build  waterworks,  an  electric  light  plant,  etc.,  so  that  no  money  for 
sewers  can  be  raised  from  bonds. 


SEWERS  AND  DRAINS  105 

(2)  The  entire  cost  of  the  sewers  may  be  assessed  against  the 
property  abutting  upon  or   adjacent  to  the  sewer.     Here  the  legal 
principle  is  that  the  assessment  must  be  in  proportion  to  the  benefit 
received.     Property  abutting  directly  upon  the  sewer  receives  the 
greatest  benefit,  and  must  be  assessed  for  most  of  the  cost.     Some- 
times the  benefit  will  be  in  proportion  to  the  number  of  feet  frontage 
of  the  lots  abutting  on  the  sewer;  and  sometimes  the  benefit  per  unit 
lot  is  considered  to  be  the  same  in  all  parts  of  the  city,  a  large  unit 
size  of  lot  being  adopted  in  the  residence  part  of  the  city,  and  a 
much  smaller  size  in  the  business  section,  with  often  an  intermediate 
size  between  these  two. 

The  "assessment"  is  levied  upon  the  completion  of  the  sewer, 
when  the  entire  cost  can  be  ascertained.  Due  notice  to  all  property 
owners  assessed  must  be  given,  so  that  they  can  present  objections 
if  they  desire.  Usually  all  property  owners  who  desire  are  allowed 
to  spread  the  payment  of  their  assessments  in  equal  installments  over 
a  considerable  period  of  years,  in  which  case  assessment  certificates 
are  issued  to  cover  the  payments.  The  contractor  is  often  required  to 
take  these  certificates  in  payment  for  the  sewer. 

(3)  The  cost  of  the  sewers  may  be  divided  between  the  City  and  the 
property  directly  abutting  upon  or  adjacent  to  the  sewer.     This  seems 
the  fairest  way ;  since,  in  the  first  place,  the  entire  city  receives  benefit 
from  improved  sanitation,  attractiveness  to  investors,  etc.,  from  a 
sewer  constructed  anywhere  within  its  limits ;  and  since,  in  the  second 
place,  any  system  of  sewers  for  a  city  should  be  planned  to  give 
outlets  of  proper  size  to  all  parts  of  the  district,  which  enlarges  and 
deepens  the  sewers  on  many  streets.     On  the  other  hand,  the  property 
along  the  sewer  is  benefited  much  more  than  the  rest  of  the  city,  and 
should  accordingly  pay  a  much  larger  proportion  of  the  cost. 

The  City  Council  usually  has  the  right  to  decide  what  percentage 
of  the  cost  is  to  be  paid  by  the  City  and  what  by  the  property  along 
the  sewers. 

PREPARATION  OF  PLANS  AND  SPECIFICATIONS  FOR  SEW- 
ERAGE SYSTEMS 

90.  Sewer  Reconnaissance.  When  a  sanitary  engineer  is 
called  upon  to  prepare  plans  and  specifications  for  a  sewerage  system, 
the  first  thing  which  he  should  do  is  to  make  a  reconnaissance  or 


106  SEWERS  AND  DRAINS 

general  study  of  the  entire  city  and  its  surroundings,  with  special 
reference  to  its  sewerage  conditions. 

He  visits  the  city  and  obtains  copies  of  the  best  maps  procurable. 
If  these  maps  do  not  show  the  contours  or  elevations  of  the  surface 
at  different  points,  he  obtains  the  best  procurable  information  as  to 
such  elevations,  and  enters  it  upon  the  maps.  Often  the  elevations 
of  street  grades  will  prove  sufficient,  if  better  and  more  detailed  in- 
formation is  lacking.  If  street  profiles  are  available,  they  will  of 
course  be  of  great  value. 

With  maps  thus  prepared  for  the  purpose,  he  rides  or  walks  over 
all  parts  of  the  city,  making  himself  thoroughly  familiar  with  its 
topography  and  other  features.  Some  of  the  information  thus 
obtained  may  be  entered  upon  the  maps.  He  will  note  the  present 
density  of  population  in  different  sections,  and  the  prospects  for  future 
growth.  The  presence  or  absence  of  manufacturing  industries,  and 
the  future  prospects  in  this  line,  are  of  importance.  Statistics  of 
the  past  growth  of  the  city  will  be  obtained.  Full  information  regard- 
ing the  character  of  the  water  supply  and  the  amount  and  fluctua- 
tions of  the  water  consumption,  and  the  distribution  of  the  water 
mains  throughout  the  city,  will  be  of  great  value.  The  local  labor 
conditions,  and  the  probable  local  cost  of  cement,  sand,  brick, 
sewer  pipe,  and  other  needed  materials,  must  be  ascertained. 
All  possible  information  should  be  secured  regarding  the  ground 
water  and  the  character  of  the  soil  in  different  sections  of  the  city. 
Information  about  old  excavations  and  about  wells  can  usually  be 
secured,  and  will  give  much  light  on  these  points. 

From  his  general  study  of  the  conditions,  including  especially 
the  topography,  the  engineer  must  decide  whether  the  system  of 
sewerage  shall  be  a  separate  system,  or  a  combined  system  (see 
Articles  10  to  13,  inclusive). 

The  question  of  the  outlet  will  be  one  of  the  most  important 
controlling  points  to  be  decided,  and  the  engineer  must  carefully 
examine  all  possibilities  in  this  line.  The  number  of  outlets  should 
be  as  small  as  feasible,  one  outlet  being  secured  if  possible.  The  outlet 
must  be  low  enough  to  drain  thoroughly  all  portions  of  the  district  it 
serves,  and  should  be  chosen  with  a  view  to  safe  and  satisfactory 
disposal  of  the  sewage. 

Sewage  disposal  is  one  of  the  very  important  points  to  be  con- 


SEWERS  AND  DRAINS  107 

sidered.  In  the  past,  most  cities  have  simply  discharged  their  sewage 
into  the  nearest  available  body  or  stream  of  water  which  it  was  con- 
sidered could  be  used  without  causing  damage  or  injunction  suits  on 
account  of  the  pollution.  At  the  present  time,  cities  are  being  com- 
pelled more  and  more  to  provide  means  for  purifying  the  sewage 
(see  Articles  110  to  124);  and  the  engineer,  in  choosing  the  outlet 
and  planning  the  sewers,  should  always  consider  it  probable  that  in 
the  not  distant  future  the  city  will  be  compelled  to  use  some  method 
of  purification,  and  his  plans  should  be  so  made  as  readily  to  permit 
this  in  the  future,  even  if  the  city  builds  no  sewage  purification  works 
at  first. 

During  the  reconnaissance,  the  engineer  must  constantly  be 
recording  the  significant  information  he  secures,  in  a  neat  and  system- 
atic manner  in  a  standard  notebook,  which  he  keeps  for  the  purpose. 
Loose-leaf  notebooks  of  pocket  size  have  many  advantages  for  this 
purpose.  In  the  same  notebook,  he  should  make  all  his  preliminary 
computations. 

On  completing  the  reconnaissance,  the  engineer  usually  makes 
a  preliminary  report  to  the  city  officers,  stating  the  conditions  he  has 
found,  and  his  conclusions  as  to  the  general  features  of  the  system 
he  has  decided  to  recommend  as  best.  He  also  usually  presents  at 
this  time  some  rough  estimates  of  cost. 

The  city  then  decides  whether  or  not  to  adopt  the  general  recom- 
mendations of  the  engineer,  and  whether  to  go  on  with  the  preparation 
of  plans  and  specifications. 

91.  Surveys  for  Sewer  Plans.  After  the  reconnaissance,  if  it 
is  decided  to  go  ahead  with  the  plans,  the  next  step  will  be  to  make 
the  necessary  surveys.  These  may  usually  be  divided  into  three 
principal  parts  as  follows: 

(1)  Surveys  of  Sewage  Disposal  Site.     In  case  a  sewage  dis- 
posal plant  is  to  be  built,  a  survey  of  the  site  must  be  made  to  secure 
the  data  needed  for  the  design.     Usually  this  will  include  data  for  a 
contour  map  of  tne  entire  tract,  and  borings  or  pits  to  determine  the 
character  of  the  soil. 

(2)  Surveys  for  the  Outlet  Sewer.    Transit  and  level  lines  must 
be  run,  and  profiles  prepared,  to  determine  the  best  route  for  the 
outlet  sewer.     Data  must  be  secured  for  an  accurate  map  and  profile 
of  the  final  location  of  this  sewer. 


108  SEWERS  AND  DRAINS 

(3)  Surveys  for  the  Street  Sewers.  Usually,  existing  plats  can 
be  found  sufficiently  accurate  to  give  the  dimensions  necessary  for 
constructing  the  general  sewerage  map,  without  special  surveys. 
Small  errors  on  these  plats  will  not  affect  the  general  design,  and 
will  not  be  of  much  importance  in  view  of  the  accurate  surveys  which 
must  be  made  later  during  construction.  Sometimes  a  few  measure- 
ments with  tape-line  and  transit  must  be  taken  in  special  localities. 
Usually  the  main  part  of  the  surveys  for  the  street  sewers  consists  in 
running  lines  of  levels  along  all  the  streets  on  which  there  is  possibility 
of  planning  sewers,  in  order  to  secure  the  data  necessary  to  make  the 
sewer  profiles  of  all  the  sewers. 

These  levels  should  be  referred  to  the  city  datum — that  is,  the 
reference  level  above  which  all  city  elevations  are  given.  If  such  a 
datum  has  not  already  been  adopted,  one  should  be  established,  and 
marked  by  a  permanent  bench-mark,  A  six-inch  iron  pipe  set  six 
feet  in  the  ground,  filled  and  surrounded  with  concrete,  makes  a  good, 
permanent  bench-mark.  The  top,  not  quite  rilled  with  concrete,  pro- 
jects a  little  above  the  ground,  and  a  copper  bolt  is  set  in  the  concrete 
at  the  top,  the  top  of  the  bolt  constituting  the  bench-mark.  The 
pipe  should  have  a  hinged  iron  cap  to  protect  the  bolt. 

In  running  the  level,  no  effort  should  be  made  to  trace  out  the 
main  lines  of  sewers  and  their  branches,  but  each  street  sjiould  be  sur- 
veyed by  itself.  A  zero  point  should  be  taken  at  some  definite  point 
(such  as  the  center  line,  or  one  of  the  side  lines,  of  a  cross-street)  at 
one  end  of  the  street,  and  station  points  100  feet  apart  determined  by 
continuous  measurements  with  a  steel  tape.  These  stations  should 
be  numbered  continuously  from  the  zero  point,  intermediate  points 
being  located,  in  the  usual  way,  by  plus  distances  from  the  preceding 
station.  Thus  station  9  +  72  is  972  feet  from  the  zero  point. 

The  exact  plus  of  each  side  line  of  each  cross-street,  and  of 
points  opposite  other  important  things,  should  be  determined  and 
recorded  in  the  notebook,  to  give  measurements  to  be  used  in  pre- 
paring the  profiles,  and  in  checking  the  map. 

All  lines  of  levels  must  be  checked.  At  the  end  of  each  street. 
the  leveling  can  be  extended  across  to  an  adjacent  street,  and  checked 
with  the  line  of  levels  on  that  street. 

Numerous  bench-marks  should  be  established  around  the  city, 


SEWERS  AND  DRAINS  109 

located  on  permanent  points,  such  as  the  tops  of  the  foundation  walls 
of  buildings. 

92.  Sewerage  Plans.  From  the  data  obtained  by  the  surveys, 
the  sewerage  plans  must  be  prepared.  These  will  usually  consist 
of  a  large  number  of  separate  sheets,  the  following  being  a  list  of  the 
sheets  of  one  particular  set  of  plans,  for  a  separate  system  of  pipe 
sewers. 

1.  Index  Sheet.     (Giving  the  contents  of  all  other  sheets.) 

2.  General  Sewerage  Map. 

3.  General  Map  of  Sewage-Disposal  Plant. 

4.  Detailed  Plans  of  Septic  Tank.     (For  the  Sewage-Disposal  Plant.) 

5.  Detailed  Plans  of  Filter  Beds.      (For  the  Sewage-Disposal  Plant.) 

6.  Plans  of  Standard  and  Drop  Manholes,  and  Lampholes. 

7.  Plans  of  Combined  Manholes  and  Flush-Tanks. 

8  to  33.     Profile  Sheets.     (Showing  profiles  of  all  the  sewers.) 

In  other  cases,  separate  sheets  may  be  needed  for  many  other 
things,  as,  for  example, 

Details  of  Brick  Sewers,  of  different  sizes. 

"  Concrete  Sewers,         "•         " 
Plans  of  Flush-Tanks. 
"      "  Catch-Basins. 
"      "  Street  Inlets. 
"      "  Sewage  Pumping  Station. 
Etc.,  etc. 

For  the  sake  of  convenience  and  of  neatness  and  system,  all  the 
sheets  of  a  set  oj  sewerage  plans  should  be  made  of  a  standard  size  (one 
or  two  can  be  made  larger  and  folded  to  the  standard  size),  and  they 
should  be  bound  together  in  regular  book  covers,  18  inches  by  24  inches 
being  a  convenient  standard  size  of  sheet  for  most  cases. 

Fig.  37  is  a  photographic  view  of  such  a  cover  containing  a  set 
of  sewerage  plans.     The  cover  protects  the  sheets  from  injury,  and 
is  so  arranged  that  any  sheet  can  readily  be  removed  and  replaced 
A  cover  like  that  shown  costs  about  $1.50. 

The  original  drawings  were  all  made  on  tracing  cloth,  except 
the  profiles,  which  were  made  on  transparent  profile  paper.  Thus 
all  the  sheets  can  readily  be  reproduced  by  the  process  of  blue-print- 
ing, and  only  the  blue-print  sheets  are  used  on  the  work  or  by  the 
City,  the  engineer  retaining  the  original  tracings  in  his  office,  where 
they  can  be  kept  safe. 

In  such  a  set  of  plans,  the  sheets  should  be  numbered  in  order 
(see  Figs.  38  and  39);  and  a  standard  title  (see  title  of  Fig.  38)  should 


110 


SEWERS  AND  DRAINS 


be  adopted  for  all  sheets  which  will  require  few  changes  of  the  dif- 
ferent sheets. 

Sewerage  Map.  In  Fig.  38  is  shown  a  reduced  copy  of  an  actual 
sewerage  map  of  a  separate  system  of  sewers  for  a  small  town.  The 
original  size  of  the  map  shown  was  36  inches  by  24  inches,  so  that 
folding  it  once  reduced  it  to  the  18-inch  by  24-inch  size. 

The  original 
scale  of  the  map 
shown  was  200 
feet  per  inch ;  but 
for  larger  places, 
300  feet  or  even 
400  feet  per  inch 
maybe  sufficient, 
since  large-scale 
maps  of  all  the 
individual  sew- 
ers appear  on  the 
profile  sheets. 

The  lines  of 
sewers  in  a  sys- 
tem such  as 

shown  in  Fig.  38,  ought  to  be  restricted  as  far  as  possible  to  the  streets 
on  which  the  lots  front.  Sewers  on  cross-streets  add  to  the  mileage 
of  sewers  without  serving  additional  lots,  and  are  useless  except  for 
connecting  other  sewers. 

The  manholes,  lampholes,  flush-tanks,  etc.,  should  be  numbered 
systematically,  something  as  shown  in  Fig.  38,  no  two  structures  of 
the-  same  kind  having  the  same  number.  This  avoids  danger  of 
duplication  where  the  same  structure  is  shown  on  two  or  more  sheets, 
as  is  often  the  case. 

Sewer  Profiles.  In  Fig.  39  is  shown  a  sample  profile  sheet  from 
an  actual  set  of  plans. 

The  original  profile  was  made  on  "Plate  B"  transparent  profile 
paper,  so  that  the  profiles  can  be  reproduced  easily  by  blue-printing, 
the  same  as  the  other  drawings.  The  sheets  were  cut  to  the  standard 
size,  18  inches  by  24  inches,  to  bind  with  the  other  drawings. 

The  profiles  should  be  made  in  systematic  order  of  the  streets,  each 


Pig.  37.    Standard  Cover  for  Sewerage  Plans. 


SEWERS  AND  DRAINS 


111 


street  completed  before  beginning  the  next,  instead  of  trying  to  follow 
up  the  main  lines  of  the  sewers  and  their  branches. 

The   profile   sheets   show   large-scale   maps   of  the   individual 


Manholes 
Lampholei 
MushTanK  <$  Manholes 
1  Street  Inlets 


PLANS     OF 

SEWERAQE   SYSTEM 

AMES.  IOWA 
QENERAL  SEWERAQE  MAP 

ORIGINAL  SCA-LEIINCH-SOOFT.     Jucv  e-i903. 
33  SHEETS 


fio"ouTLCT  3  ewe  A 


Fig.  38. 

sewers  immediately  below  their  profiles,  to  permit  the  exact  location 
of  manholes,  etc.,  and  of  the  sewer  itself  in  the  street. 

93.  Specifications  for  Sewers.  Besides  the  plans,  it  will  be 
necessary  for  the  sewerage  engineer  to  prepare  precise  instructions 
regarding  all  matters  of  importance  not  fully  shown  by  the  plans, 


112 


SEWERS  AND  DRAINS 


likely  to  come  up  during  the  construction  of  any  part  of  the  sewerage 
system.     Such  instructions  are  called  Specifications. 

An  ordinary  set  of  sewer  specifications  will  consist  of  three  parts : 

(1)  A  Notice  to  Contractors,  or  form  of  advertisement  for  the  city  officers, 
to  use  in  advertising  for  bids. 

(2)  A  Form  for  Proposal,  with  suitable  blanks,  on    copies  of  which, 
furnished  by  the  city,  all  contractors  are  required  to  make  their  bids. 


Fig.  39.    Typical  Sewer  Profile  Sheet. 

(3)  The  Specifications  Proper.  These  again  will  consist  of  two  main 
divisions : 

(a)  General  clauses,  relating  to  payments,  guarantees,  etc.,  and  to 
general  features  of  the  work. 

(6)  Specific  clauses,  specifying  the  exact  details  of  different  parts  ol  the 
work. 

A  copy  of  an  actual  set  of  specifications  for  the  construction  of 
a  separate  system  of  pipe  sewers,  with  a  sewage-disposal  plant,  is 
given  herewith: 

CITY  OF , 

SPECIFICATIONS 

FOR 

SEWERS  AND  SEWAGE-DISPOSAL  PLANT 

NOTICE  TO  CONTRACTORS 
The    Incorporated    City    of , .,    will    reseiva 


SEWERS  AND  DRAINS  113 

sealed  bids  until , ,  at  -  ;;  (1)  for  the 

construction  of  a  sewage-disposal  plant,  consisting  of  a  sewage  tank  of  about 

gals,  capacity,  and sand  filter  beds,  each  of  about sq.  ft. 

area;  and  (2)  for  the  construction  of  sewers  as  follows:  about ft.  of  18- 
inch,  ft.  of  15-inch, ft.  of  12-inch, ft.  of  10-inch,  and ft. 

of  8-inch,  with  suitable  appurtenances,  all  in  accordance  with  plans  and  speci- 
fications prepared  by ,  Engineer, ,  and  now  on 

file  in  his  office  and  with  the  City  Clerk.  All  bids  must  be  accompanied  with 
certified  checks,  approximately  in  the  amount  of  5  per  cent  of  the  bid,  made 

payable  without  recourse  to  the  City  of , .     The  City 

reserves  the  right  to  reject  any  or  all  bids,  to  waive  defects,  and  to  accept 
any  bid.  All  bids  must  be  in  sealed  envelopes,  marked  on  the  outside 
"Sewerage  Bids,"  and  addressed  to ,  City  Clerk. 

INSTRUCTIONS  TO  BIDDERS,  AND  GENERAL  SPECIFICATIONS 

(1)     Items.     The  items  of  work  intended  to  be  covered  by  these  specifi- 
cations are  those  required  for  the  entire  completion  of  the  System  of  Sanitary 

Sewers  for  the   City  of , , 

according  to  the  plans  prepared  by '• — : ,  Engineer,  and  include 

the  following: 

(a)     The  construction  of  a  Sewage-Disposal  Plant,  including  a  sewage 

tank  of  about gallons  capacity,  and sand  filter  beds,  each  of  about 

sq.  ft.  area,  and  including  all  valves,  sewer  pipes,  outlets,  etc. 

(6)     The  construction  of  Sewers  as  follows: 

18-inch Ft. 

15-inch 

12-inch " 

10-inch " 

8-inch " 

Manholes " 

Lampholes " 

Combined  Manholes  and  Flush-Tanks,         " 

together  with  subdrains  as  directed  by  the  City. 

(2)  Application.     These    general    specifications    and    instructions    to 
bidders  shall  apply  to  all  items  of  workmanship  or  materials  enumerated  above 
or  hereinafter  mentioned. 

(3)  Definitions  of  Terms.     Wherever  the  word  "City"  is  used  in  these 

specifications,  it  shall  be  understood  to  mean  the  Incorporated  City  of , 

.,  acting  through  the  Mayor  and  Council,  or  their  duly  authorized  repre- 
sentatives.    Wherever  the  word  "Contractor"  is  used  in  these  specifications, 
it  shall  be  understood  to  mean  the  person  or  firm  employed  to  do  all  or  any 
part  of  the  work  or  furnish  all  or  any  part  of  the  material  for  the  Sanitary 
Sewerage  System.     Wherever  the  word  "Engineer"  is  used  in  these  specifi- 
cations, it  shall  be  understood  to  mean  the  Engineer  employed  by  the  City 
to  design  or  supervise  the  construction  of  all  or  any  part  of  the  Sanitary  Sewer- 
age System. 

(4)  Bids.     All  bids  must  be  on  blanks  furnished  by  the  City  for  the 
purpose.     The  blanks  can  be  obtained  from ,  City  Clerk 

or  from ,   Engineer, . 


114  SEWERS  AND  DRAINS 

All  bids  must  be  enclosed  in  sealed  envelopes  addressed  to , 

City  Clerk, , .,  and  plainly  marked  on  the  outside  with  the 

words  "Sewerage  Bids." 

Each  bid  must  be  accompanied  with  a  certified  check  approximately  in 
the  sum  of  5  per  cent  of  the  bid,  and  made  payable  without  recourse  to  the 
City  Treasurer, , —  — . 

The  City  reserves  the  right  to  reject  any  or  all  bids,  to  waive  defects,  and 
to  accept  any  bid. 

(5)  Certified  Checks.     The  certified  check  mentioned  above  will  be 

forfeited  as  damages  to  the  Incorporated  City  of—  — ,  — ., 

unless  the  Contractor  enters  into  contract  and  furnishes  bonds  satisfactory 
to  the  Mayor  and  Council  within  12  days  after  the  contract  has  been  awarded 
to  him.     Certified  checks  not  so  forfeited  shall  be  returned  to  the  bidders  as 
soon  as  the  contract  is  signed  and  satisfactory  bonds  are  furnished. 

(6)  Bond.     A  bond  satisfactory  to  the  Mayor  and  Council  shall  be 
furnished  by  the  Contractor,  approximately  in  the  amount  of  50  per  cent  of  the 
contract  price. 

(7)  Time.     The  Contractor  shall  begin  work  within  3  weeks  after 
the  contract  is  awarded  to  him,  and  shall  entirely  complete  the  work  on  or 
before ,  —  — . 

(8)  Sub-contracts.     No    sub-contracts    shall    be    awarded    to    parties 
unacceptable  to  the  City. 

(9)  Progress  of  the  Work.     The  work  shall  be  prosecuted  at  a  rate  to 
enable  its  completion  within  the  time  specified;  and  should  the  Contractor 
fail  to  do  this,  the  City  may,  after  giving  ten  days'  written  notice,  take  over 
the  work  and  complete  it  at  the  Contractor's  expense. 

(10)  Penalties.     Should  the  Contractor  fail  to  complete  the  work  at 
the  time  specified,  he  shall  forfeit  to  the  City  a  sum  equal  to  all  damages  to  it 
resulting  from  the  failure  to  complete  the  work  at  the  time  specified. 

(11)  Delays.     No  claims  for  damages  shall  be  made  against  the  City 
on  account  of  delays  in  delivery  of  materials  or  performance  of  work ;  but 
should  there  be  unduly  prolonged  delays  in  the  delivery  of  any  materials  or 
the  performance  of  work  on  the  part  of  the  City, the  Contractor  shall  be  entitled 
to  corresponding  extension  of  time. 

(12)  Obstructions.     The  Contractor  shall  carry  on  the  work  in  such  a 
way  as  to  obstruct  the  city  streets  as  little  as  possible,  and  so  as  not  at  any 
time  entirely  to  shut  off  passage  of  teams  and  pedestrians  at  any  place.     He 
shall  provide  temporary  crossings  satisfactory  to  the  City  for  this  purpose 
wherever  necessary. 

(13)  Precautions.     The  Contractor  shall  take  all  necessary  precautions 
to  prevent  injury  to  the  public  or  to  his  workmen  or  to  stock,  such  as  providing 
crossing  plank,  fencing  off  his  work,  keeping  lanterns  burning  at  night,  etc.  He 
shall  hold  the  City  harmless  against  all  claims  for  damages. 

(14)  Plans  and  Specifications.     The  City's  plans  and  these  specifications 
shall  be  a  part  of  the  contract,  and  all  materials  and  workmanship  shall  be  in 
accordance  with  them. 

(15)  Supervision.     All  materials   and  workmanship   shall  be   subject 
to  the  supervision  and  inspection  of  the  City  and  of  its  Engineer  or  other  author- 
ized representative.     Instructions  as  to  the  details  of  the  work  shall  be  carried 


SEWERS  AND  DRAINS  115 

out,  and  rejected  materials  and  work  shall  be  promptly  removed  at  any  time 
discovered. 

(16)  Quality  of  Materials  and  Workmanship.     All  workmanship   and 
materials  shall  be  of  the  best  quality. 

(17)  Quantities.     The  quantities  named  in  the  notice  to  contractors, 
the  form  of  proposal,  or  in  these  specifications,  are  approximate  only.     The 
City  shall  have  the  right  to  vary  them;  and,  if  so  varied,  the  total  contract 
price  shall  be  increased  or  diminished  at  the  rates  named  per  unit  in  the  con- 
tract. 

(18)  Extra  Work.     No  extra  work  shall  be  done  without  written  orders 
from  the  City  or  its  specially  authorized  representatives  placed  in  charge  of 
the  work.     In  case  extra  work  becomes  necessary,  it  shall  be  done  by  the  Con- 
tractor if  so  ordered,  and  shall  be  paid  for  by  the  City  on  the  basis  of  actual 
cost,  plus  10  per  cent;  but  no  extra  work  will  be  paid  for  unless  ordered  in 
writing  by  the  proper  authority  at  the  time  undertaken. 

(19)  Changes  in  Plans.     The  City  shall  have  the  right  to  make  changes 
in  plans.     In  making  such  changes,  the  unit  prices  named  in  the  contract  shall 
be  used,  as  far  as  possible,  in  calculating  the  changes  in  price  on  account  of 
changes  in  the  plans,  and  where  these  do  not  apply,  the  changes  in  price,  unless 
a  special  agreement  between  the  City  and  the  Contractor  as  to  prices  is  made 
at  the  time  the  changes  are  ordered,  shall  be  calculated  on  the  same  basis  as 
extra  work. 

(20)  Claims.     The  Contractor  shall  guarantee  the  payment  of  all  just 
claims  for  materials  or  labor  in  connection  with  his  contract.     Preliminary  to 
the  payment  for  any  work,  he  shall,  if  required  by  the  City,  present  evidence 
satisfactory  to  the  Mayor  and  Council  that  all  bills  for  materials  and  labor  have 
been  paid,  and  any  or  all  payments  may  be  reserved  until  such  evidence  has 
been  presented.     If  the  payment  of  any  just  claim  shall  be  deferred  more  than 
four  weeks  after  written  notice  has  been  given  concerning  it  to  the  Contractor, 
the  City  may  proceed  to  pay  such  claim  out  of  any  money  due  the  Contractor. 

(21)  Payments.     Payments  shall  be  made  as  follows: 

(NOTE:  Fill  in,  in  this  blank,  whether  the  payment  is  to  be  made  in  cash,  in  sewer 
warrants,  sewer  certificates,  or  otherwise.  Also  whether  payments  are  to  be  made 
monthly  as  the  work  progresses,  or  reserved  until  completion,  the  former  plan  being 
usual  for  cash  payments,  and  the  latter  for  payments  in  certificates.) 

All  payments  shall  be  on  estimates  prepared  by  the  Engineer  and  ap- 
proved by  the  Council,  of  materials  delivered  and  work  performed;  and  in  case 
of  all  payments  made  prior  to  the  completion  of  the  contract,  15  per  cent  of 
the  estimate  shall  be  reserved  until  the  final  payment  on  completion  of  the 
work. 

No  payment  shall  be  considered  as  releasing  the  Contractor  from  obliga- 
tion to  remove  and  make  good  defective  work  and  materials  when  discovered 
at  any  time. 

Two  per  cent  of  the  total  cost  may  be  reserved  by  the  City  for  one  year 
after  the  completion  of  the  work,  and  any  part  of  this  reserve  may  be  used  to 
make  good  defects  developed  within  that  time  from  faulty  workmanship  and 
materials,  provided  that  notice  shall  first  be  given  the  Contractor,  and  that  he 
may  promptly  make  good  such  defects  himself  if  he  desires. 


116  SEWERS  AND  DRAINS 

(22)  Guarantee.     The  Contractor  shall  guarantee  the  workmanship  and 
materials  for  one  year,  and  keep  the  system  in  repair  after  completion,  as 
provided  in  clause  21  above. 

(23)  Risks.     All  materials  and  work  will  be  at  the  risk  of  the  Contractor 
until  the  final  acceptance  of  the  same. 

(24)  Cleaning  Up.     On  completion  of  each  part  of  the  work,  all  rubbish 
and  unsightly  materials  must  be  removool  and  disposed  of  as  directed  by  the 
City,  and  the  streets  and  grounds  left  in  neat  condition.     For  the  sewers,  each 
two  blocks  must  be  cleaned  up  immediately  on  completion,  and  on  the  com- 
pletion of  the  entire  contract  shall  be  further  put  in  good  shape  if  needed. 

MATERIALS 

(25)  Vitrified  Sewer  Pipe.    All  sewers  shall,  unless  special  permission 
be  given  to  use  cement  sewer  pipe,  be  constructed  of  first-quality  salt-glazed, 
vitrified  clay  sewer  pipe,  of  the  hub-and-spigot  pattern,  of  standard  thick- 
nesses and  dimensions  of  hubs.     The  dimensions  of  hubs  shall  be  sufficient  to 
leave  an  annular  space  for  cement  of  at  least  f-inch  thickness  for  8-inch  and 
10-inch  pipe,  and  £-inch  thickness  for  larger  diameters. 

Pipe  may  be  furnished  in  lengths  of  2,  2£,  or  3  feet.  All  pipe  and  specials 
shall  be  sound  and  well  burned,  with  a  clear  ring,  well  glazed  and  smooth  on 
the  inside,  and  free  from  broken  blisters,  lumps,  or  flakes  which  are  thicker 
than  £  the  nominal  thickness  of  the  pipe  and  whose  largest  diameters  are 
greater  than  ^  the  inner  diameter  of  said  pipe ;  and  the  pipe  and  specials  having 
broken  blisters,  lumps,  and  flakes  of  any  size  shall  be  rejected  unless  the  pipe 
can  be  so  laid  as  to  bring  all  of  these  defects  in  the  top  half  of  the  sewer.  No 
pipe  having  unbroken  blisters  more  than  £  inch  high  shall  be  used,  unless  these 
blisters  can  be  placed  in  the  top  half  of  the  sewer.  Pipes  or  specials  having 
fire-checks  or  cracks  of  any  kind  extending  through  the  thickness  shall  be 
rejected. 

No  pipe  shall  be  used  which,  designed  to  be  straight,  varies  from  a  straight 
line  more  than  ^  inch  per  foot  of  length;  nor  shall  there  be  any  variation  be- 
tween any  two  diameters  of  a  pipe  greater  than  -^  the  nominal  diameter. 

No  pipe  shall  be  used  which  has  a  piece  broken  from  the  spigot  end  deeper 
than  1£  inches  or  longer  at  any  point  than  \  the  diameter  of  the  pipe;  nor 
which  has  a  piece  broken  from  the  bell  end  if  the  fracture  extends  into  the  body 
of  the  pipe,  or  if  such  fracture  cannot  be  placed  at  the  top  of  the  sewer.  Any 
pipe  or  special  which  betrays  in  any  manner  a  want  of  thorough  vitrification 
or  fusion,  or  the  use  of  improper  or  insufficient  materials  or  methods  in  its 
manufacture,  shall  be  rejected. 

(26)  Sewer-Pipe  Specials.     All  T-  and  Y-  junction  curves,  etc.,  required 
shall  be  furnished  and  set  without  extra  charge,  and  shall  conform  to  the  pipe 
specifications  as  to  quality.     Y's  for  house  connections  may  be  required  every 
25  feet  on  the  average,  and  shall  be  closed  by  vitrified  stoppers  cemented  over 
sand. 

(27)  Drain-Tile.     All    drain-tile    shall   be   best-quality   vitrified   agri- 
cultural drain-tile  in  one-foot  lengths.     All  junctions  and  inspection  openings 
shall  be  made  with  suitable  T-  and  Y-  junctions  and  curves,  furnished  and  set 
without  extra  charge. 


SEWERS  AND  DRAINS  117 

(28)  Brick.     All  brick  used  on  the  work  shall  be  sound,  partially  vitri- 
fied, well-shaped  brick,  equal  to  No.  2  paving  brick. 

(29)  Cement.     All  cement  used  shall  be , ,  ,  ,  , 

,  or Portland  Cement,  perfectly  fresh,  and  not  damaged  in  any  particu- 
lar.    It  shall  be  subject  to  the  Standard  specifications  of  the  American  Society 
for  Testing  Materials,  and  will  be  rejected  if  it  does  not  meet  these  require- 
ments.    All  cement  shall  also  be  subject  to  close  inspection  as  it  is  used   01. 
the  work,  and  damaged  cement  will  be  rejected  and  must  be  promptly  removed. 

(30)  Sand.     All  sand  shall  be  clean,  sharp,  and  coarse.     All  sand   for 
mortar  for  sewer  joints  or  brick  masonry  must  have  all  pebbles  screened  out. 

(31)  Broken  Stone  and  Pebbles.     The  aggregate  for  concrete  shall   con- 
sist of  either  broken  stone  or  screened  pebbles  passing  a  2|-inch  ring  for  ordi- 
nary concrete,  and  a  1^-inch  ring  for  the  septic  tank.     The  materials   must 
be  sound  and  hard  and  durable.     The  sand  must  be  screened  out  of  pebbles 
used;  but  the  fine  materials  need  not  be  screened  out  from  broken  stone,  a  re- 
duction being  made  in  the  amount  of  sand  used,  approximately  equal  to   the 
amount  of  stone  dust. 

(32)  Cast  Iron.     All  cast  iron  shall  be  good,  tough,  gray  iron,  free  from 
defects.     Castings  shall  be  smooth  and  free  from  blowholes  or  other  flaws. 

(33)  Cast-Iron  Water-Pipe.     All  cast-iron  pipe  shall  be  cast  of  the  hub- 
and-spigot  pattern,  of  standard  weights  for  water-pipe  for  light  pressures.     The 
pipe  shall  be  well  coated. 

(34)  Valves.     All  valves  shall  be  iron  body,  brass-mounted,  hub-end, 
double-gate,  water  valves,  well  coated,  of  the  —  —  or  of  equal  make 
acceptable  to  the  Engineer. 

(35)  Valve  Boxes.     All  valve  boxes  shall  be  —  extension 

boxes  with  5^-inch  shafts,  or  some  equal  make  acceptable  to  the  Engineer. 

MORTAR  AND  CONCRETE 

(36)  Mortar.     All  mortar  for  brickwork  or  other  masonry  shall  be  made 
of  one  part  of  Portland  cement  to  three  parts  of  sand;  and  all  mortar  for  sewer 
joints,  of  one  part  of  cement  to  one  of  sand,  both  ingredients  being  measured 
loose  and  thoroughly  mixed.     All  mortar  shall  be  mixed  fresh  as  used,  and 
any  mortar  which  has  begun  to  set  shall  be  thrown  away  and  not  used  at  all 
on  the  work. 

(37)  Concrete.    All  masonry  shown  on  the  plans  to  be  made  of  con- 
crete shall  be  constructed  with  Portland  cement,  sand,  and  either  broken 
stone  or  screened  pebbles  passing  a  2^-inch  ring,  in  the  proportions  1-3-5  for 
ordinary  work,  and  l-2-3£  for  the  septic  tank,  the  cement  being  measured 
packed  as  it  comes  in  sacks  or  barrels,  and  the  sand  being  measured  loose  as 
thrown  into  the  measuring  box  with  shovels.     The  proportions  shall  be  deter- 
mined by  suitable  measuring  boxes,  or  by  the  use  of  wheelbarrows.     In  case 
of  hand-mixing,  the  sand  and  cement  shall  first  be  thoroughly  mixed  dry  until 
the  color  of  the  mixture  is  uniform.     They  shall  then  again  be  mixed  with 
water,  and  then  again  with  the  freshly  wet  aggregate,  each  mixing  being  very 
thorough,  and   sufficient  to  secure  perfect  mixture  of   the  materials.      If  a 
machine  mixer  is  used,  it  shall  be  of  a  make  acceptable  to  the  Engineer,  and 
shall  be  so  used  as  to  give  very  thorough  mixing.     Just  enough  water  shall  be 


118  SEWERS  AND  DRAINS 

used  to  make  the  concrete  slightly  quake  when  thoroughly  rammed,  the  water 
freely  flushing  to  the  surface  under  the  ramming. 

In  depositing,  the  material  shall  be  deposited  in  layers  not  exceeding 
6  inches  in  height,  and  thoroughly  rammed.  Where  work  is  left  for  the  night, 
the  layers  shall  be  racked  back.  Where  fresh  concrete  is  deposited  on  work 
which  is  already  set  or  begun  to  set,  the  surface  shall  first  be  thoroughly  cleaned 
and  wet,  and  washed  with  a  coat  of  liquid  neat  cement.  After  the  concrete 
is  deposited,  great  care  shall  be  taken  not  to  disturb  it  until  the  work  is  thor- 
oughly set.  The  work  shall  be  protected  from  the  sun,  and  shall  be  wet  from 
time  to  time,  until  it  is  thoroughly  set. 

TRENCHING,  PIPE-LAYING,  REFILLING,  ETC. 

(38)  Excavation.     The  excavation  shall  be  made  exactly  to  line  and 
grade  as  indicated  by  stakes  set  by  the  Engineer.     At  the  bottom,  the  trench 
shall  have  a  clear  width  at  least  one  foot  greater  than  the  external  diameter 
of  the  body  of  the  pipe.      The  last  four  inches  shall  be  excavated  only  a  few 
feet  in  advance  of  the  pipe-laying,  by  men  especially  skilled,  measuring  from 
an  overhead  line  set  parallel  to  the  grade  line  of  the  sewer.      The  bottom  of 
the  trench  shall  be  rounded  to  fit  the  pipe ;  and  holes  shall  be  dug  for  the  bells 
so  as  to  give  a  uniform  bearing,  and  permit  the  proper  construction  of  the  sewer 
joints  on  the  under  side  of  the  pipe.     The  earth  taken  from  the  trench  shall  be 
deposited  neatly  at  the  sides,  in  such  manner  as  to  obstruct  the  streets  as 
little  as  possible ;  and  a  clear  space  of  two  feet  next  the  trench  shall  be  left  on 
the  side  on  which  the  Engineer  places  his  stakes.     Great  care  shall  be  taken  to 
preserve  and  not  to  cover  up  the  Engineer's  stakes. 

(39)  Sheathing.     Wherever  necessary  to  prevent  caving  of  the  banks 
or  injury  to  adjacent  pipes  or  buildings,  the  Contractor  shall,  at  his  own  expense, 
brace  and  sheath  the  trenches  sufficiently  to  overcome  the  difficulty  to  the 
satisfaction   of  the  Engineer.     If  such  bracing  and  sheathing  is  left  perma- 
nently in  the  trench  by  order  of  the  Engineer,  it  shall,  on  refilling,  be  cut  off  one 
foot  below  the  surface  and  shall  be  paid  for  by  the  City  at  the  price  named  in 
the  contract;  but  otherwise  the  Contractor  will  receive  no  extra  compensa- 
tion for  it. 

(40)  Water  in  Trenches.     In  general,  all  water  encountered  in  trenches 
must  be  drained  away  through  the  sub-drains  or  pumped  or  bailed  out,  and 
the  trench  must  be  kept  dry  for  the  pipe-laying.     In  no  case  shall  the  sewers 
be  used  as  drains  for  such  water,  and  the  ends  of  the  sewer  shall  be  kept  prop- 
erly blocked  during  construction.     All  necessary  precautions  shall  be  taken 
by  the  Contractor  to  prevent  the  entrance  of  mud,  sand,  or  other  obstructing 
material  into  the  sewers  or    subdrains;  and  on  completion  of  the  work,  any 
such  materials  wriich  may  have  entered  must  be  cleaned  out  and  the  sewers  and 
subdrains  left  clean  and  unobstructed. 

(41)  Refilling.     In  refilling,  earth  free  from  stones  shall  be  carefully 
placed  by  hand  under  and  around  the  pipe  and  to  the  height  of  two  feet  above 
the  top  of  the  sewer,  and  thoroughly  and  carefully  rammed  in  layers  of  not 
more  than  six  inches'  depth. 

The  remainder  of  the  refilling  shall  be  carefully  done.  Scrapers  may  be 
used  if  desired.  The  refilling  shall  be  thoroughly  flooded  by  the  Contractor 
according  to  the  direction  of  the  Engineer,  the  City  furnishing  the  water  free 


SEWERS  AND  DRAINS  119 

at  the  hydrant ;  but  the  refilling  shall  be  carried  on  in  such  a  way  that  water 
is  taken  only  as  directed  by  the  Waterworks  Superintendent,  and  so  that  not 
more  than gallons  of  water  shall  be. required  in  any  one  day. 

Where  the  trench  is  not  flooded,  it  shall  be  left  neatly  rounded  off  on  top 
to  a  height  of  twice  as  many  inches  as  the  top  width  of  the  trench  in  feet; 
and  the  City  may  from  the  2  per  cent  reserve  make  good  any  settlement  below 
the  street  surface  within  one  year  from  the  date  of  completion,  notice  being 
first  given  the  Contractor,  who  may  promptly  do  the  work  himself  if  he  desires. 

All  surplus  material  shall  be  removed  to  such  point  within  the  limits 
of  the  sewer  district  as  may  be  designated  by  the  City;  and  in  case  of  defi- 
ciency of  material,  it  shall  be  supplied  by  the  Contractor.  The  street  surface 
shall  be  left  in  neat,  sightly  condition. 

(42)  Foundations.     In  case  the  material  encountered  should  be  such 
as  not  to  be  suitable  for  foundations  for  the  sewer,  the  Engineer  shall  direct 
the  character  of  foundations  to  be  constructed,  and  this  shall  be  paid  for  by 
the  City  as  extra  work. 

(43)  Protection  to  Buildings.     The  Contractor  shall  take  all  necessary 
precautions  to  protect  building  and  other  structures  adjacent  to  the  sewer 
trenches  from  injury  on  account  of  his  work,  and  shall  be  responsible  for  all 
damages  to  such  structures. 

(44)  Existing  Sewer  and  Water  Mains.     Wherever  existing  sewers  or 
water  mains  are  encountered  in  the  work,  all  necessary  precautions  shall  be 
taken  to  prevent  injury  to  them;  and  in  case  of  an  injury,  it  shall  be  made 
good  by  the  Contractor  without  additional  compensation.     In  case  any  sewer, 
drain,  or  water  main  should  be  encountered  whose  present  grade  should  require 
changing  on  account  of  the  new  sewers,  the  work  necessary  for  this  shall  be 
performed  by  the  Contractor  according  to  the  directions  of  the  Engineer,  and 
shall  be  paid  for  as  extra  work. 

(45)  Pipe-Laying.     In  pipe-laying,  each  piece  must  be  set  exactly  to 
grade  by  measuring  from  the  invert  to  a  tightly  stretched  cord  set  parallel 
to  the  grade  line,  according  to  stakes  or  marks  given  by  the  Engineer,  and  sup- 
ported at  least  every  25  feet.     In  making  each  joint,  a  gasket  of  oakum  or 
hemp  freshly  dipped  in  cement  grout  must  first  be  used  and  packed  into  place, 
so  as  to  make  the  inverts  match  exactly,  giving  a  smooth,  true  flow-line.     The 
joints  shall  afterwards  be  tightly  packed  full  and  beveled  off  with  1  to  1  Portland 
cement  mortar;  but  tne  cementing  must  be  done  at  least  two  pipe  lengths 
behind  the  pipe-laying.     The  bell-holes  must  then  be  immediately  packed 
with  sand  to  hold  the  cement  in  place.     Great  care  must  be  taken  to  leave  no 
projecting  cement  or  strings  of  gaskets  on  the  inside  of  the  sewer,  and  to  make 
all  joints  as  nearly  water-tight  as  possible.      Especial  care  must  be  taken  in 
forming  the  joint  on  the  under  side  of  the  pipe. 

(46)  House  Connections.     At  points  indicated  by  the  Engineer  opposite 
each  lot,  and  at  such  other  points  as  may  be  indicated  by  the  Engineer,  4-inch 
Y's  shall  be  laid,  with  the  branch  tilted  up  at  an  angle  of  about  45°.     These 
shall  be  furnished  and  laid  without  extra  charge,  up  to  an  average  of  one  in 
each  25  feet. 

At  points  indicated  by  the  Engineer,  deep-cut  house  connections  shall 
be  put  in  according  to  the  plans.  The  City  shall  pay  for  these  the  regular 
contract  price. 


120  SEWERS  AND  DRAINS 

In  both  ordinary  and  deep-cut  house  connections,  the  connection  shall 
be  closed  by  a  vitrified  stopper  filled  over  with  sand  and  lightly  cemented. 

(47)  Subdrains.      Wherever    directed    by    the    City,    drain-tile    sub- 
drains  of  diameters  directed  by  the  Engineer  shall  be  constructed.     Each 
drain  shall  be  laid  just  at  one  side  of  the  sewer,  at  a  depth  below  the  sewer 
invert  equal  to  the  external  diameter  of  the  subdrain,  plus  three  inches.     Each 
joint  shall  be  wrapped  twice  with  a  4-inch  strip  of  muslin  at  the  time  laid. 
The  subdrains  shall  be  laid   carefully  to  line  and  grade;  and  wherever  the 
Engineer  may  direct,4-inch  Y's  stopped  with  brick  shall  be  placed.     In  general, 
these  Y's  will  be  placed  at  the  same  points  as  the  house  connections  on  the 
sewer. 

(48)  Subdrain    Outlets.      Wherever    directed    by    the    Engineer,    sub- 
drain  outlets  shall  be  constructed,  also  as  directed  by  the  Engineer,  and  shall 
be  paid  for  by  the  City  on  the  basis  of  cost  as  determined  by  the  Engineer, 
plus  10  per  cent. 

(49)  Measurements.      All    measurements    of    sewers,    subdrains,    etc., 
shall  be  in  horizontal  lines  from  center  to  center  of  manholes  and  junctions. 

MANHOLES  AND  OTHER  APPURTENANCES 

(50)  Manholes.     Manholes  shall  be  constructed  as  shown  on  the  plans 
and  provided  in  these  specifications,  the  exact  location  being  indicated  by  the 
Engineer.     All  joints  in  the  brickwork  shall  be  shove  joints,  being  filled  full. 
Especial  care  shall  be  taken  in  forming  the  channels  in  the  concrete  bottoms, 
and  wooden  templates  or  half -sewer-pipe  shall  be  used  for  this  work,  as  directed 
by  the  Engineer.     Drop  manholes  shall  be  constructed  as  shown  on  the  plans 
without  additional  charge  over  the  price  bid,  which  shall  be  considered  an 
average  price. 

(51)  Combined  Manholes  and  Flush-Tanks.     Combined  manholes  and 
flush-tanks   shall  be  constructed  as  shown  on  the  plans  and  as  specified  for 
manholes  in  clause  50.     The  siphons  shall  be  carefully  set,  and  the  cost  of 
furnishing  and  setting  shall  be  included  in  the  price  bid.     The  Contractor  shall 
provide  and  set  the  water  connection  and  bibbs  from  a  point  one  foot  outside 
the  outside  wall,  on  such  side  as  the  Engineer  may  direct. 

(52)  Siphons.     Siphons  shall  be  used  as  shown  on  the  plans,  guaranteed 
by  the  manufacturers,  and  tested  after  being  set  before  acceptance.     For  the 
8-  and  10-inch  sewers,  6-inch  siphons  shall  be  used,  and  8-inch  for  all  sewers 
larger  than  10  inches. 

(53)  Lampholes.     Lampholes   shall   be   constructed   as   shown   on   the 
plans  and  provided  in  these  specifications,  the  exact  locations  being  indicated 
by  the  Engineer.     The  refilling  shall  be  carefully  placed  and  thoroughly  rammed 
by  hand  in  layers  not  exceeding  6  inches,  around  and  to  a  distance  of  three 
feet  each  side  of  each  lamphole.     Special  pains  shall  be  taken  to  keep  the 
'ampholes  truly  vertical. 

SPECIFICATIONS  FOR  SEWAGE-DISPOSAL  PLANT 

(54)  Grading.     All  grading  shall  be  done  as  shown  by  the  plans.     The 
bottom  of  the  filter  beds  and  bottom  and  sides  of  the  septic  tank  shall  be  shaped 
to  true  surfaces  by  hand.     All  slopes  shall  be  neatly  dressed. 

Should  there  be  a  deficiency  of  earth  for  the  embankments,  the  Contractor 


SEWERS  AND  DRAINS  121 

may  borrow  from  neatly-shaped  borrow  pits  located  on  adjacent  city  land, 
where  directed  by  the  Engineer,  leaving  a  smooth,  uniform  surface.  Should 
there  be  surplus  material,  it  shall  be  deposited  along  the  edge  of  the  lake,  as 
directed  by  the  Engineer. 

(55)  Concrete  Moulds.     The  Contractor  shall  provide  moulds  of  plank 
not  less  than  two  inches  in  thickness,  thoroughly  braced  at  intervals  sufficiently 
close  together  to  avoid  distortion  of  the  moulds.     These  planks  shall  be  dressed 
on  their  edges  and  on  the  faces  next  to  the  wall.     The  moulds  shall  not  be 
removed  until  the  walls  have  become  thoroughly  set. 

(56)  Facing  of  Concrete  Walls.     In  the  construction  of  concrete  walls, 
care  shall  be  taken  to  keep  all  pebbles  or  stones  away  from  the  faces  of  the 
walls,  so  that  the  face  shall  be  smooth  and  free  from  cavities  or  exposed  stones 
or  pebbles.     The  upper  surface  of  the  roof  shall  be  floated  with  1-2  thin  mortar 
applied  when  the  roof  is  made,  and  all  cavities  in  other  concrete  surfaces  filled 
and  smoothed  with  1-2  mortar. 

(57)  Cement  Wash.     On  completion  of  concrete  walls  and  floors,  and 
after  removal  of  the  moulds  and  pointing  up  defects,  all  interior  surfaces  of 
floors  and  walls  and  roof,  and  the  upper  surface  of  the  roof,  shall  be  given  two 
good  coats  of  thin,  neat  Portland    cement  grout  applied  with  a  whitewash 
brush,  time  being  left  between  applications  for  the  first  coat  to  set  hard. 

(58)  Alternating  Siphons.     The  alternating  siphons  shall  be  provided 
of  the  make  shown  on  the  plans,  and  set  by  the  Contractor,  strictly  according 
to  the  directions  of  the  manufacturer  as  given  through  the  Engineer.     Any 
imperfections  affecting  the  working  of  the  siphons  when  they  are  tested  shall 
be  corrected  by  the  Contractor, who  must  guarantee  their  satisfactory  working. 

(59)  Filters.    The  pebbles  for  the  bottoms  of  the  filters  shall  be  screened 
clean  of  sand  and  properly  graded,  the  2-inch  layer  of  fine  pebbles  being  small 
enough  to  hold  up  the  sand  placed  over  it.     All  sand  shall  be  clean  and  coarse, 
but  the  pebbles  need  not  be  screened  out.     In  placing  pebbles  and  sand,  care 
shall  be  taken  not  to  injure  or  disturb  the  drain  tile,  and  the  top  surface  of 
the  sand  shall  very  carefully  be  made  level.     Drain  tile  shall  be  laid  carefully 
to  line  and  grade. 

(60)  Pipe-Laying.     All  sewer  pipe  and  cast-iron  pipe  shall  be  carefully 
laid  to  line  and  grade,  with  gaskets  and  tight  joints,  all  as  provided  in  the  regu- 
lar sewer  specifications. 

(61)  Sodding.     All  earthwork  slopes  of  the  tank  and  filters  shall  be 
neatly   sodded. 

(62)  Bulkheads.     All    bulkheads    shown    on    the   plans    shall    be    con- 
structed of  Portland  cement  concrete,  with  moulds,  and  with  care  as  to  facing 
the  same  as  provided  for  the  concrete  work  of  the  septic  tank. 

(63)  Reinforcing.     The  reinforcing  shown  on  the  plans  is 

corrugated  bars  of  not  less  than  50,000  Ibs.  per  sq.  in.  elastic  limit;  but  other 
forms  of  bars  having  equal  elastic  limit,  equal  net  area,  and  a  mechanical  bond 
acceptable  to  the  Engineer,  may  be  used.     The  net  area  of  any  bars  used  must 
be  increased  to  make  good  any  deficiency  in  the  elastic  limit. 


122  SEWERS  AND  DRAINS    • 

For  brick  sewers,  the  following  specifications  are  suggested  by 
Folwell  in  his  book  on  Sewerage: 

"For  brick  masonry  in  straight  walls  or  sewers,  none  but  whole,  sound 
brick  shall  be  used.  For  manholes,  flush-tanks,  and  similar  work,  a  limited 
number  of  half -brick  may  be  used,  not  to  exceed  ^  of  the  whole  in  any  case. 
Unless  the  Engineer  direct  otherwise,  each  brick  shall  be  thoroughly  wetted 
immediately  before  being  laid.  It  shall  be  laid  with  a  full,  close  joint  of  cement 
mortar  on  its  bed,  ends,  and  side  at  one  operation.  In  no  case  is  mortar  to 
be  slushed  in  afterward.  Special  care  shall  be  taken  to  make  the  face  of  the 
brickwork  smooth;  and  all  joints  on  the  interior  of  a  sewer  shall  be  carefully 
struck  with  the  point  of  a  trowel  or  pointed  to  the  satisfaction  of  the  Engi- 
neer. Where  pipe-connections  enter  a  sewer  or  manhole,  "bull's-eyes"  shall 
be  constructed  by  laying  rowlock  courses  of  brick  around  them,  the  cost  of 
such  construction  being  included  in  the  regular  price  bid  for  the  sewer  or 
appurtenances.  Around  pipe  more  than  15  inches  in  diameter,  2  rowlock 
courses  shall  be  laid. 

"Brickwork  in  sewers  shall  be  laid  by  line,  each  course  perfectly  straight 
and  parallel  to  the  axis  of  the  sewer.  Joints  appearing  in  the  sewer  shall  in 
no  case  exceed  \  inch  in  width.  Sewers  shall  conform  accurately  in  section 
and  dimensions  to  the  plans  of  the  same.  All  inverts  and  bottom  curves  shall 
be  worked  from  templates'  accurately  set ;  the  arches  are  to  be  formed  upon 
strong  centers  accurately  and  solidly  set,  and  the  crowns  keyed  in  full  joints 
of  mortar.  No  centers  shall  be  drawn  until  the  arch  masonry  has  set  to  the 
satisfaction  of  the  Engineer,  and  refilling  has  progressed  up  to  the  crown. 
They  shall  be  drawn  with  care,  so  as  not  to  crack  or  injure  the  work.  The 
extrados  is  to  be  neatly  plastered  with  cement  mortar  £  inch  thick,  the  arches 
being  cleaned  and  wetted  just  before  plastering.  The  end  of  each  section  of 
brick  sewer  shall  be  toothed  or  racked  back;  and  before  beginning  the  suc- 
ceeding section,  all  loose  brick  at  the  end  shall  be  removed  and  the  toothing 
cleaned  of  mortar.  All  brickwork  shall  be  thoroughly  bonded,  adjacent 
courses  breaking  joints  at  least  %  the  exposed  length  of  the  brick. 

"If  there  should  be  any  distortion  of  the  sewer  before  acceptance,  this 
shall  be  corrected  by  tearing  down  and  rebuilding.  No  local  patching  will  be 
allowed,  but  when  repairs  are  necessary  a  section  shall  be  removed  at  least 
3  feet  long  and  including  the  entire  arch,  or  the  entire  sewer  if  the  defect  is 
in  the  invert.  Leakage  of  ground  water  into  the  sewer  shall  be  similarly  cor- 
rected, unless  it  can  be  prevented  by  calking  the  joints  with  oakum  saturated 
in  cement,  with  wooden  plugs,  or  other  material  acceptable  to  the  Engineer." 

FORM  OF  PROPOSAL 


To  the  Mayor  and  Council  of  the  Incorporated  City  of — 

*  Gentlemen: 

—  have  carefully  examined  the  plans  and  read  the  specifi- 
cations prepared  for  your  proposed  sewage-disposal  plant  and  sanitary  sewers 

by 1  Engineer,  and agree  to  furnish  all  the  materials  and  perform 

all  the  labor  required  for  the  completion  of  the  proposed  work  for  the  following 
prices: 


SEWERS  AND  DRAINS 


123 


ITEM 

APPROXIMATE 
QUANTITY 

UNIT  PRICE 

TOTAL  PRICE 

Sewaoe  Disposal  Plant   cornpl6t6    .  . 

Sewers,  complete,  including  Y's,  except 
subdrains,  manholes,    lampholes, 
and  flush-tanks. 
18-inch     

15-inch       

12-inch 

10-inch  

8-inch       

Subdrains,  complete 
10-inch  

8-inch  

Deep-Cut  House  Connections,  complete  . 
Manholes  complete    

Combined  Manholes  and  Flush-Tanks, 
complete                      

Lumber  Left  in  Trenches  (per  M.,  B.  M.) 

All  the  above  shall  be  strictly  in  accordance  with  the  plans  and  specifi- 
cations. 

In  case bid  is  accepted, agree  to  begin  work  within  three  weeks 

after  the  acceptance  of  -     -  bid,  and  to  entirely  complete  the  work  on  or 
before , 

further  agree  to  enter  into  contract  and  furnish  bond  satisfactory 

to  the  City  Council  within  12  days  after  acceptance  of bid. 

Respectfully  submitted, 


94.  Form  for  Sewerage  Contract.  Besides  plans  and  specifica- 
tions, the  sewerage  Engineer  is  sometimes  called  upon  to  furnish  a 
Form  of  Contract  to  be  signed  by  the  Contractor  and  the  city  repre- 
sentatives, though  this,  more  properly,  should  be  the  work  of  the 
City  Attorney.  The  following  simple  form  of  contract  has  been  used 
successfully  with  specifications  such  as  those  given  above : 

©Ijia  Arttrl*  of  Agrrmwti,  made  this  —  —  day  of  - 

A.D., ,  by  and  between ,  of  -  — , , 

party  of  the  first  part,  and  the  Incorporated  City  of  -      — ,  —  — ,  acting 
through  its  Mayor  and  Council,  party  of  the  second  part, 

WlTNESSETH ! 

The  party  of  the  first  part  agrees  to  furnish  all  material  and  perform  all 
labor  required  for  the  entire  completion  of  sanitary  sewers,  subdrains,  and  other 
appurtenances,  on  streets  in  the  said  City  of  —  — ,  —  — ,  as  follows : 

(NOTE:  In  this  space  place  a  list  of  the  sewers  included  in  the  contracts  by 
streets,  giving  the  sizes  on  each  street  of  both  sewer  and  subdrain,  and  the  points  at 
which  each  size  begins  and  ends.) 


124  SEWERS  AND  DRAINS 

All  the  above  sewers  are  to  have  manholes  and  other  appurtenances  as 
shown  by  the  plans  and  specifications. 

The  party  of  the  first  part  further  agrees  that  all  the  above  labor  and 
materials  shall  be  strictly  in  accordance  with  the  sewer  plans  and  specifica- 
tions prepared  for  the  party  of  the  second  part  by  —  — ,  Engineer, 
said  plans  and  specifications  identified  by  the  signatures  of  the  parties  hereto, 
being  hereby  made  a  part  of  this  contract. 

The  party  of  the  second  part  agrees  to  pay  to  the  party  of  the  first  part 
for  the  above  labor  and  materials,  the  following  prices : 
Sewers,  complete,  except  subdrains,  manholes, 
lampholes,  and  flush-tanks, 

24-inch $  per  lin.  ft. 

20     "  "      " 

18     "    "      " 

15     "    "      " 

12     "    "      " 

10     "    .  "      " 


Subdrains,  complete, 

24-inch 
18     " 
15     " 
12     " 
10     " 


Manholes,  complete $  each 

Lampholes,  complete " 

Combined  Manholes  and  Flush-Tanks,  complete " 

Flush-Tanks,  complete " 

Lumber  ordered  left  in  trenches $  per      M.,  B.  M. 

The  payments  shall  be  made  in — 

— and  paid  to  the  party  of  the  first  part  in  accordance 

with  the  provisions  of  the  specifications,  2  per  cent  being  reserved  for  one  year 
to  guarantee  the  vrork. 

IN  WITNESS  WHEREOF  we  have  hereunto  "set  our  hands  and  seals  the 
date  and  place  first  above  mentioned. 


Party  of  the  First  Part 
SEAL 

The  Incorporated  City  of  —          — ,  by 

— Mayor, 

SEAL 


Party  of  the  Second  Part 

95.  Form  of  Bond  for  Sewerage  Contract.  The  Contractor 
for  a  piece  of  sewerage  work  is  usually  required  to  furnish  to  the  City 
a  bond,  which  is  frequently  for  a  sum  equal  to  about  one-half  the 


SEWERS  AND  DRAINS  125 

amount  of  the  contract.     The  simpler  the  form  of  the  bond,  the  better. 
The  following  form  has  been  used  successfully: 

BOND 

KNOW    ALL    MEN    BY    THESE    PRESENTS,    that    W6, • ,    Of 

— ,  Principal,  and 


Sureties 

are  held  and  firmly  bound  to  the  Incorporated  City  of  —  — , , 

in  the  penal  sum  of —        Dollars  ( ), 

lawful  money  of  the  United  States  of  America. 

Now,  THE  CONDITION  OF  THIS  OBLIGATION  is  that  whereas  the    above- 
mentioned  ,   of , ,   has   entered  into 

contract  with  the  Incorporated  City  of , ,  dated .,  A.  D. , 

to  furnish  all  labor  and  materials  required  for  the  entire  completion  of  about 

feet  of  sanitary  sewers,    subdrains,  and  other  appurtenances  for   the 

said  City  of , ,  now,  if  the  said ,  shall 

well  and  truly  perform  all  the  obligations  of  his  said  contract,  strictly  according 
to  the  terms  thereof,  then  shall  this  bond  be  null  and  void,  but  otherwise  it 
shall  be  and  remain  in  full  force  and  effect. 


Principal 


Sureties 

CONSTRUCTION  OF  SEWERS 

96.  Letting  the  Sewer  Contract.  After  the  plans  and  specifica- 
tions have  been  completed  and  accepted  by  the  City,  the  next  step 
will  be  to  let  the  contract  for  the  work. 

First.  The  work  should  be  advertised,  if  possible,  three  or  four  weeks  in 
advance,  in  at  least  two  good  engineering  or  trade  journals.  It  must  often, 
by  law,  be  advertised  also  in  at  least  one  local  journal.  For  a  form  for  the 
advertisement  see  pages  112  and  113. 

Second.  On  the  day  and  at  the  hour  specified  in  the  advertisements, 
the  City  Council  meets  to  open  the  sealed  bids  which  have  been  submitted  on 
the  blank  "forms  for  proposals"  furnished  by  the  City  for  the  purpose. 

Third.  If  the  bids  are  satisfactory,  the  contract  is  awarded  to  the 
lowest  responsible  bidder. 

Fourth.  A  contract  for  executing  the  work  in  accordance  with  the  plans 
and  specifications,  is  signed  by  the  Contractor  and  by  the  City. 

Fifth.     The  Contractor  furnishes  a  bond  satisfactory  to  the  City. 

In  all  these  steps,  there  is  need  of  great  care  on  the  part  of  the 
city  authorities  to  make  sure  that  all  provisions  of  the  law  are  com- 


126  i     SEWERS  AND  DRAINS 

plied  with,  and  they  should  be  fully  advised  at  all  times  by  a  com- 
petent attorney. 

97.  Organization  of  Engineering  Force  during  Construction  of 
Sewers.  It  is  not  common  for  the  Consulting  Engineer  who  pre- 
pares the  sewerage  plans  and  specifications,  to  be  constantly  on  the 
ground  or  even  in  the  city  during  construction.  He  makes  only 
occasional  visits  for  inspection  and  consultation. 

The  actual  work  of  sewer  construction  is  usually  directly  super- 
vised either  by  the  City  Engineer,  or  by  a  Resident  Engineer  employed 
especially  for  this  purpose. 

It  will  be  necessary  for  the  resident  engineer  in  charge  of  the  con- 
struction of  a  sewerage  system  of  some  magnitude,  to  have  an  office 
and  an  adequate  equipment  of  drafting  apparatus,  surveying  instru- 
ments, etc.  He  will  have  employed  under  him : 

Draftsmen  and  clerks,  in  the  office. 

Instrument  men  and  rodmen,  to  do  the  surveying. 

Inspectors,  constantly  on  all  work,  to  insure  its  being  properly  executed. 

The  resident  engineer  himself  will  supervise  these  employees, 
visit  all  parts  of  the  work  frequently,  and  constantly  exercise  general 
supervision  over  all  its  features. 

98.  Laying  Out  the  Sewer  Work.  After  checking  up  the  bench- 
marks on  the  original  survey,  it  will  be  necessary  for  the  engineering 
force  to  stake  out  the  sewers,  keeping  somewhat  in  advance  of  the 
actual  construction. 

The  stakes  are  usually  placed  a  uniform  distance  to  one  side  of 
the  true  line,  so  as  not  to  be  disturbed  by  the  digging  of  the  trench. 
This  distance,  and  the  side  on  which  the  stakes  are  placed,  should  be 
the  same  for  all  parts  of  the  work,  to  avoid  confusion  and  mistakes. 

The  stakes  should  usually  be  set  about  25  feet  apart. 

The  manholes  should  usually  be  located  first,  in  accordance 
with  the  profile  sheets;  and  the  sewers  should  be  run  as  straight  lines, 
center  to  center  of  adjacent  manholes.  All  discrepancies  from  the 
original  measurements  should  each  be  adjusted,  if  possible,  between 
the  two  manholes  between  which  each  was  found;  and  such  dis- 
crepancies should  not  be  carried  on  to  affect  all  the  rest  of  the  work. 

There  are  two  methods  of  giving  grades  for  sewers. 

(1)  The  best  method  is  to  set  the  grade  stakes  nearly  flush  with 
the  surface,  at  a  uniform  offset  to  one  side  of  the  trench,  ascertaining 


SEWERS  AND  DRAINS  127 

the  distance  of  the  top  of  each  stake  above  grade  by  carefully  checked 
levels.  By  measuring  from  these  stakes,  a  grade  cord,  supported 
on  cross-frames  every  25  feet,  is  stretched  parallel  to  the  grade  line 
of  the  sewer,  over  its  center  line.  For  this  method  of  giving  grades, 
see  Fig.  40. 

(2)  Another  method  is  to  set  grade  stakes  at  the  bottom  of  the 
trench.  This  method  is  adapted  only  to  very  large  sewers. 

99.  Trenching  and  Refilling.  Sewer  trenching  and  refilling 
may  be  done  either  by  machines  or  by  hand.  Excavating  Machines 
for  sewers  are  of  two  types : 

(1)  Machines  which  themselves  do  the  excavating.     These  are 
just  coming  into  use,  and  are  becoming  more  and  more  successful. 

(2)  Machines  which  simply  carry  away  the  excavated  material, 
usually  dumping  it  over  the  completed  sewer  further  back.     This 
type  has  the  advantage  of  not  piling  up  the  dirt  in  the  busy  street. 
It  carries,  on  overhead  cableways  or  trestles,  buckets  which  can  be 
lowered  into  the  trench,  and  in  which  the  excavated  material  is  placed 
by  hand. 

Machines  of  both  types  are  suited  best  to  comparatively  extensive 
work;  and  under  favorable  conditions  they  lessen  the  cost  materially. 

Most  sewer  trenching,  however,  is  done  by  hand.  For  such 
work  the  men  are  organized  in  gangs,  the  number  of  men  in  each 
gang  varying  from  20  to  80.  Each  gang  has  a  foreman,  and  a  water 
boy,  and  sometimes  a  sub-foreman.  A  pair  of  pipe-layers  may  work 
with  each  gang,  or,  if  the  trench  be  deep,  one  pair  of  pipe-layers  may 
work  part  of  the  time  with  one  gang  and  part  with  another. 

The  details  of  sewer  trenching  and  refilling  as  ordinarily  carried 
out,  are  specified  quite  fully  in  clauses  38,  40,  and  41  of  the  sample 
sewer  specifications  given  in  Art.  93  (which  clauses  now  read  carefully). 
All  details  there  specified  should  be  enforced  by  the  Inspector  and  the 
Engineer. 

In  clause  41,  Art.  93,  referred  to  above,  the  method  specified  for 
compacting  the  refilling  is  by  flooding  with  water.  While  this  is  the 
cheapest  method,  where  the  water  is  available,  and  while  it  gives  good 
results  if  properly  done,  it  may  be  found  necessary  sometimes,  in 
the  case  of  paved  streets,  to  adopt  the  more  expensive  method  of 
tamping.  For  thorough  tamping,  there  should  be  from  1  to  2  men 
tamping,  to  1  shoveler,  and  the  rammers  used  should  weigh  4  to  6 


128 


SEWERS  AND  DRAINS 


pounds  each.  The  soil  refilled  should  be  moistened  if  dry,  and  should 
be  tamped  in  about  4-inch  layers.  It  is  possible  by  very  thorough 
tamping  to  compact  the  soil  more  thoroughly  than  by  flooding. 

100.  Sheathing.  Except  for  shallow  ditches  in  very  solid  earth, 
it  is  usually  necessary  to  brace  the  sides  of  sewer  trenches  to  prevent 
their  caving  in.  Such  bracing  is  called  sheathing.  The  most  com- 
mon methods  of  sheathing  are  illustrated  in  Fig.  40. 

The  horizontal  members  of  the  sheathing  are  called  rangers, 
and  the  rangers  are  held  the  right  distances  apart  by  sewer  braces  of 

wood  or  iron.  The 
iron  braces  are 
shown  in  Fig.  40. 
The  rangers  are 
usually  about  12 
feet  long.  Behind 
the  range;rs  are 
placed  the  vertical 
planks  of  the 
sheathing,  either  a 
few  feet  apart  in 
firm  material,  form 
ing  skeleton  sheath- 
ing, or  in  contact 
with  each  other  in 
caving  material, 
forming  close 
sheathing.  The 


Pipe  with  Hemp  Gasket 
Ready  for  Lowering 


Bell  Ho 


-Sewer  Pipe 

S-ub  Drain 

Bottom  of  Trench  Shaped 
To  Fit  Bo<ly  of  Sewei-  Pipe 


Fig.  40.    Diagram  Showing  Construction  of  Pipe  Sewer. 


sheathing  plank  are  2  inches  thick  and  are  usually  about  10  feet  or 
12  feet  long.  The  rangers  may  be  2-inch  planks  in  favorable  soil>  or 
4  by  4  or  even  4  by  6  inches  in  poor  soil. 

The  sheathing  plank  are  usually  driven  by  hand,  with  wooden 
mauls. 

Sometimes,  for  large  sewers,  heavy  sheet  piling  may  be  driven 
by  pile-drivers,  to  take  the  place  of  ordinary  sheathing. 

Ordinary  sheathing  is  removed  from  the  trench  as  the  refilling 
proceeds.  In  case  of  special  danger  to  near-by  water  mains,  conduits, 
or  foundations,  on  account  of  possibility  of  the  banks  caving  before 
the  refilling  is  finally  settled,  the  Engineer  may  order  the  sheathing 


SEWERS  AND  DRAINS  129 

to  be  left  permanently  in  the  trench.  In  such  case,  the  Inspector 
makes  record  of  the  exact  amount  of  lumber  left  in  the  trench,  and 
the  City  pays  for  it. 

101 .  Pipe-Laying.  The  pipe-laying  is  usually  done  by  two  men* 
though,  with  large  pipes,  another  may  be  needed.     These  men  exca- 
vate the  last  few  inches  of  the  trench,  as  well  as  lay  the  pipes. 

The  laying  of  every  pipe,  and  the  making  of  every  joint,  should  be 
carefully  watched  by  an  Inspector^  who  should  faithfully  enforce  the 
specifications. 

For  specifications  for  pipe-laying,  see  clause  45,  Art.  93  (which 
clause  now  read  carefully). 

All  the  sewer  pipe  should  be  carefully  inspected  before  being 
used,  and  those  pieces  rejected  which  do  not  meet  the  specifications. 
See  clause  25,  Art.  93.  The  Inspector  should  see  that  no  rejected 
or  poor  pipe  is  used. 

The  Inspector  should  see  that  every  pipe  is  laid  exactly  to  grade 
by  measurement  from  the  grade  cord  (see  Fig.  40). 

The  Inspector  should  also  see  that  house-connection  Y's  are 
placed  opposite  each  lot  on  each  side  of  the  street,  at  the  proper  points; 
and  he  must  exactly  locate  each  such  connection  by  measurements 
fully  recorded  in  his  notebook. 

102.  Construction  of  Brick  Sewers.    For  specifications  for  the 
construction  of  brick  sewers,  see  reference  to  Folwell  in  Art.  93,  p.  122. 
(Read  carefully.) 

The  construction  of  a  brick  sewer  is  shown  in  Fig.  41. 

It  will  be  the  duty  of  the  Inspector  to  inspect  all  brick  before  they 
are  used,  rejecting  the  poor  ones,  and  to  fully  enforce  the  specifica- 
tions for  construction.  He  must  also  see  that  the  templates  are  set 
truly  to  line  and  grade,  that  the  house  connections  are  set  at  the  proper 
places  and  heights,  and  accurately  located  in  his  records. 

In  the  case  of  large  brick  sewers,  more  trouble  is  to  be  expected 
with  foundations  than  in  the  case  of  pipe  sewers.  Sometimes  soft 
soil  or  quicksand  may  make  it  almost  impossible  to  shape  the  material 
in  the  bottom  to  fit  the  outside  of  circular  sewers.  In  such  cases, 
special  foundations,  such  as  shown  in  Fig.  20,  may  have  to  be  put  in 
through  the  treacherous  material.  Other  forms  of  special  founda- 
tions are  often  used. 


130 


SEWERS  AND  DRAINS 


The  Engineer  should  make  full  record  of  all  such  features  of  the 
work. 

103.  Records  of  Sewer  Construction.  Daily  Reports.  The 
resident  Engineer  in  charge  of  the  construction  of  a  sewerage  system, 
should  require,  from  all  members  of  his  engineering  force,  daily 
reports,  on  suitable  blank  forms,  showing  the  exact  work  on  which 
each  was  engaged.  Another  set  of  exact  reports  should  show  the 
work  accomplished  by  the  Contractor  each  day,  and  the  materials 
and  labor  used  on  each  part  of  the  work. 

Data  of  Sewer  Construction.  The  information  from  these  daily 
reports  should  be  entered  in  a  permanent  book,  showing  all  features 


Comstr-ucticm  of  Ivtvert 
Fig.  41.    Diagrams  Showing  Const/ruction  of  Brick  Sewer. 


Cer\te-r  Fo-r  Sewer 
Arch 


of  the  progress  of  the  work,  and  giving  data  for  itemized  estimates 
of  the  cost. 

Sewer  Record  Book.  In  another  permanent  book,  a  complete, 
final  record  of  all  the  sewers  should  be  entered. 

On  the  left-hand  page  may  be  given  in  order  the  numbers  of  the 
stations  of  the  sewer  survey,  running  from  the  bottom  to  the  top  of 
the  page,  together  with  the  surface  elevations,  the  grade  elevations, 
and  the  rate  of  grade. 

The  exact  character  of  the  soil  should  also  be  shown,  with  exact 
levels  for  computing  any  rock  excavation.  Notes  should  be  made 
of  the  level  and  amount  of  any  ground  water  encountered. 

On  the  right-hand  page  should  be  made  a  large-scale  sketch  of 
the  sewer,  showing  its  exact  location  with  reference  to  the  street  lines 


SEWERS  AND  DRAINS  131 

and  the  lot  lines,  and  the  exact  location  of  manholes  and  other  acces- 
sories. This  sketch  should  also  show  the  location  of  all  house  con- 
nections, with  exact  measurements  (such  as  the  station  and  plus  of 
each  connection)  by  which  to  locate  all  such  connections. 

On  the  right-hand  page  may  also  be  entered  the  exact  limits 
of  sheathing  left  in  trenches,  and  the  amounts  of  lumber  in  such 
sheathing,  as  well  as  the  exact  limits  and  character  of  all  special  sewer 


Fig.  42.    Construction  of  Dry*Run  Concrete  Sewer,  Waterloo;  Iowa. 

foundations,  of  changes  of  grade  where  other  conduits  are  crossed, 
and  of  all  other  extra  work. 

Final  Sewerage  Map  and  Profiles.  On  completion  of  the  system, 
the  resident  Engineer  should  make  a  complete  final  sewerage  map, 
and  complete  final  profiles  of  all  sewers,  both  corrected  by  any  changes 
from  the  original  plans  adopted  during  construction. 

Plat  of  Sewer  Connections.  For  small  towns,  at  least,  large-scale 
plats  of  the  different  streets  should  be  prepared,  showing  the  exact 
location  of  all  house  connections. 


132  SEWERS  AND  DRAINS 

MAINTENANCE  OF  SEWERS 

104.  Sewerage  Systems  should  be  Carefully  Maintained  in  Good 
Condition.    Too  often  it  appears  to  be  considered  that  when  a  sewer- 
age system  is  completed  all  further  care  of  it  can  be  neglected  with 
impunity.     This  is  a  great  mistake.     The  sewerage  system  may 
become  a  source  of  danger  to  the  public  health,  instead  of  a  means  of 
safety,  unless  it  is  given  proper  care  and  attention. 

105.  Sewer   Ordinances,    Permits,   and    Records.    Every   city 
having  sewers  should  pass  a  carefully  prepared  Sewer  Ordinance, 
prescribing  in    detail  the  conditions  under  which  citizens  are  per- 
mitted to  use  the  sewers. 

One  provision  of  the  Sewer  Ordinance  should  be,  that  all  prop- 
erty owners  desiring  to  make  sewer  connections  shall  first  secure  a 
Sewer  Permit.  For  this"  and  for  the  application  for  it,  blank  forms 
are  provided,  which  are  to  be  filled  in  by  the  applicant,  giving  full 
description  of  the  connection.  The  permit  will  require  the  work  to 
be  done  according  to  the  city  regulations. 

Every  house  sewer  should  be  connected  with  the  sewer  at  a 
regular  house  connection.  No  cutting  into  the  sewer  whatever  should 
be  permitted,  as  there  is  great  danger  of  such  cutting  ruining  the  sewer. 

Full  Sewer  Records  should  be  kept  by  the  proper  city  officers, 
showing  full  details  of  all  connections  with  the  sewers.  This  is  too 
often  neglected,  to  the  great  detriment  of  the  City,  which  finds  itself 
without  means  of  ascertaining  what  people  or  how  many  are  using 
the  sewers,  and  perhaps  putting  injurious  substances  into  them. 

106.  Plumbing    Regulations,   Tests,   and   Licenses.    The   city 
should    also    prescribe  by  ordinance  strict   Plumbing  Regulations, 
setting  forth  in  full  detail  the  requirements  for  good  plumbing  (see 
Articles  76  to  81  inclusive).     All  property  owners  should  be  required 
to  do  all  plumbing  in  strict  accordance  with  these  regulations. 

The  work  should  be  carefully  inspected  and  tested  by  a  City 
Inspector,  to  see  that  it  fully  complies  with  the  ordinance.  The 
water  test  is  applied  by  stopping  up  the  outlets  of  the  soil-pipe  and 
of  the  various  fixtures,  and  filling  the  pipes  with  water,  when  defects 
will  be  shown  by  leaks.  In  the  smoke  test,  the  pipes  are  blown  full  of 
smoke;  and  in  the  peppermint  test,  oil  of  peppermint  is  poured  into 
them.  In  neither  case  must  it  be  possible  to  detect  any  of  the  odor 
in  the  interior  of  the  house. 


SEWERS  AND  DRAINS  133 

Plumbing  regulations  usually  require  that  plumbing  shall  be 
done  only  by  plumbers  holding  plumbers'  licenses  granted  by  the  City. 
The  proper  city  officers  have  blank  forms  for  making  applications  for 
such  licenses,  as  well  as  for  the  licenses  themselves.  The  plumber 
making  application  for  a  license  should  be  required  to  show  proof  of 
proficiency,  and  should  be  placed  under  bond  to  comply  fully  with 
the  sewer  ordinance  and  the  plumbing  regulations,  and  to  protect 
the  City  from  damages  on  account  of  his  work.  The  plumber  may 
also  'be  made  subject  to  fines  for  violating  the  sewer  ordinance  and 
regulations,  and  to  revocation  of  his  license. 

107.  Regular  Sewer  Inspection.     In  sewer  maintenance,  besides 
the  work  of  granting  sewer  permits,  and  inspecting  house  plumbing 
and  the  making  of  connections  with  the  sewers,  the  entire  sewerage 
system  should  be  gone  over  regularly  and  carefully  by  a  Sewer 
Inspector,  once  every  two  weeks  if  possible. 

The  Inspector,  in  this  work,  should  open  all  manholes  and 
lampholes,  and  carefully  examine  the  sewer  to  make  sure  that  it  is 
keeping  clean,  well-ventilated,  and  reasonably  free  from  offensive 
odors.  He  should  also  examine  carefully  the  working  of  all  flush- 
tanks,  to  make  sure  that  they  are  operating  satisfactorily.  He  should 
also  examine  all  catch-basins,  to  make  sure  that  they  are  cleaned 
frequently  enough. 

Small  defects  found  on  these  periodical  inspections  should  be 
remedied  at  once,  and  full  notes  made  of  more  extensive  work  found 
to  be  necessary. 

108.  Flushing  and  Cleaning    of   Sewers.    In  many  sewerage 
systems,  it  is  found  impossible  to  prevent  absolutely  the  formation 
of  deposits  in  the  sewers,  which  must  then  be  removed  by  hand- 
flushing,  or  by  direct  cleaning  of  the  sewers. 

Flushing  is  ordinarily  preferred  to  hand-cleaning  methods  where 
the  water  for  the  purpose  is  available,  and  where  it  is  readily  possible 
to  remove  the  deposits  in  this  way.  For  the  most  common  methods 
of  hand-flushing,  see  Art.  25. 

In  hand-cleaning,  large  sewers  may  be  entered  by  the  workmen 
themselves  to  remove  the  deposits.  In  small  sewers,  lines  are  often 
floated  down  from  one  manhole  to  the  next  below;  and  by  means  of 
these  lines,  various  cleaning  devices  are  dragged  through  the  sewer, 
or  back  and  forth  in  it,  to  remove  the  deposits.  Sometimes,  for  small 


134  SEWERS  AND  DRAINS 

sewers,  a  ball,  a  little  smaller  than  the  sewer,  with  a  line  attached  to 
haul  it  back  in  case  of  stoppage,  is  allowed  to  float  down  the  sewer, 
from  manhole  to  manhole.  The  sewage  is  dammed  back  by  it,  and 
spurts  out  on  all  sides  under  pressure,  thus  scouring  and  cleaning 
the  sewer. 

For  large  sewers,  discs  or  gates,  traveling  on  carriages,  or  boats, 
may  be  used,  working  on  the  same  principle.  Many  forms  of  such 
apparatus  have  been  devised.  A  notable  example  of  the  use  on  a 
large  scale  of  traveling  sewage-scouring  gates  is  in  connection  with  the 
Paris  sewers,  Fig.  24. 

109.  Cleaning  of  Catch-Basins.    In  Art.  27,  catch-basins  were 
described;  and  it  was  stated  that  unless  they  are  frequently  cleaned 
they  become  filled  with  filth  and  soil  and  debris  from  the  street,  and 
fail  utterly  in  their  purpose,  which  is  to  keep  such  materials  out  of 
the  sewers.     Moreover — which  is  still  worse  than  this — uncleaned 
catch-basins  are  unsanitary,  and  are  sources  of  foul  odors.     Hence 
catch-basins,  when  used,  should  be  regularly  cleaned,  and  the  City 
should  have  a  regular  arrangement  for  this  work,  and  should  provide 
labor-saving  apparatus  for  the  work,  such  as  hoisting  apparatus  or 
special  pumps  for  lifting  the  material  from  the  catch-basins  to  the 
wagons. 

SEWAGE  DISPOSAL* 

110.  Basic  Principle.    The  subject  of  sewage  disposal  seems 
prosaic  at  first  glance,  but  when  one  considers  that  its  processes 
involve  the  whole  cycle  of  life,  the  study  of  it  becomes  most  inter- 
esting.    The  organic  matters  with  which  we  have  to  deal  must  be 
changed  from  the  unstable  form  in  which  they  exist  to  stable  chem- 
ical compounds.     This  result  is  obtained  by  the  action  of  millions 
of  micro-organisms  called  bacteria.     "Without  them",  as  Woodhead 
says,  "the  surface  of  the  earth  would  be  covered  with  dead  organic 
matter,  the  remains  of  plant  and  animal  bodies,  which,  retaining 
the  elements  necessary  for  the  building  up  of  new  plant  life  and 
animal  bodies,  would  soon  cut  off  the  food  supply  of  new  plants 
and  animals;  life  would  be  impossible  because  the  work  of  death 
would  be  incomplete,"  or,  as  Pasteur  puts  it,  "because  the  return 
to  the  atmosphere  and  to  the  mineral  kingdom  of  all  that  which 
has  ceased  to  live  would  be  totally  suspended." 

*The  following  sections  on  Sewage  and  Garbage  Disposal  have  been  supplied  by  Thos. 
Fleming,  Jr.,  of  Chester  and  Fleming,  Hydraulic  and  Sanitary  Engineers,  Pittsburgh,  Pa. 


SEWERS  AND  DRAINS  135 

111.  Historical.  It  was  not  until  the  middle  of  the  nineteenth 
century  that  sewage  disposal  was  studied  or  put  into  effect  in  a 
systematic  way.  Previous  to  that  time,  it  had  been  the  habit 
of  individuals  and  communities  to  dispose  of  their  sewage  in  a 
manner  the  least  expensive  and  yet  consistent  with  preventing  a 
local  nuisance,  and  in  most  cases  where  sewer  systems  had  been 
installed,  this  resulted  in  discharging  the  sewage  into  the  nearest 
water  course.  In  communities  not  fortunate  enough  to  have 
sewer  systems,  cesspools  were  abundant,  and  in  many  instances 
were  arranged  with  overflows  to  the  nearest  surface  drain.  In 
1858,  conditions  became  so  acute  in  England,  with  its  small  streams 
and  large  tributary  population,  that  a  law  was  passed  prohibiting 
the  pollution  of  rivers,  and  during  the  next  few  years  several  able 
commissions  were  appointed  by  the  Government  to  study  the 
problem.  The  commissions  invariably  declared  that  the  proper 
method  for  purifying  sewage  was  to  distribute  it  on  land,  although 
during  this  period  private  companies  were  exploiting  chemical 
processes  and  endeavoring  to  have  chemical  precipitation  adopted 
as  the  proper  form  for  sewage  disposal.  The  disposal  of  sewage 
by  broad  irrigation  was  carried  out  on  an  extensive  scale  in  England 
during  the  latter  part  of  the  nineteenth  century,  and  several  exten- 
sive chemical  precipitation  plants  were  also  installed.  Germany 
soon  followed  England  in  prohibiting  the  discharge  of  unpurified 
sewage  into  the  streams  and  in  adopting  broad  irrigation  and 
chemical  precipitation  for  treating  it.  America  followed  shortly, 
especially  in  New  England,  as  there  the  small  streams  and  dense 
population  made  the  conditions  quite  similar  to  those  in  England. 

In  1886,  the  State  of  Massachusetts  passed  an  act  preventing 
river  pollution  and  placing  the  control  of  the  streams  in  the  hands 
of  the  State  Board  of  Health.  This  Board  constructed  an  experi- 
ment station  at  Lawrrence,  where  extensive  tests  were  made  in 
the  use  of  artificial  filters,  leading  to  the  construction  of  the  modern 
biological  filters.  Numerous  experimental  stations  followed  in 
England  and  Gemany,  which  resulted  in  many  permanent  instal- 
lations on  a  large  scale  of  artificial  biological  works. 

In  1896,  the  so-called  septic  tanks  were  developed  quite 
extensively  in  England,  and,  in  the  last  few  years,  the  settling 
tanks  with  separate  digestion  compartments  have  come  into 


136 


SEWERS  AND  DRAINS 


TABLE  XIV 
Composition  of  Sewage 


PARTS  PER  MILLION 

SUSPENDED 
SOLIDS 

NITROGEN  AS 

OXYGEN  CON- 
SUMED 

ANALYSES  OF 

S3 

RAW  SEWAGE 

1 

u 

o 

3. 

§ 

£ 

o 

S 

OJ 

"1 

'2 

d 

' 

rt 

U 

aj 

o 

•fi 

c3 
h 

33 

a 

S 

03 

_o 

O 

H 

£ 

0 

O 

h 

2 

1?5 

H 

i 

Q 

f 

u 

Atlanta,  Ga. 

285 

138 

126 

128 

188 

01 

22 

90.6 

Columbus,  O. 

209 

130 

79 

9.0 

11.0 

0.09 

0.20 

510 

25.0 

26.0 

65 

Waterbury,  Conn. 

165 

50 

115 

148 

7.8 

0.14 

1.52 

46.0 

20.0 

26.0 

41 

48 

Philadelphia,  Pa. 

189 

59 

130 

6.3 

4.0 

0.23 

1.00 

760 

35.6 

40.4 

128 

39 

prominence  together  with  methods  for  the  disinfection  of  sewage 
and  the  removal  of  suspended  matter  by  fine  screens. 

SEWAGE 

112.  Character    of    Sewage.    The    average    sewage    consists 
mainly  of  water  used  for  washing  and  flushing  purposes.     In  America, 
the  daily  water  consumption  ranges  from  thirty  gallons  to  four 
hundred  gallons  per  capita  with  an  average  of  one  hundred  gallons 
per  capita.     This  water,  in    passing   through  the    sewer  system, 
contains  a  variable  amount  of  solids  and  liquids  representing  the 
\vaste  products  of  the  community  which  altogether  does  not  exceed 
two  per  cent  of  the  water.     If  analyzed  bacteriologically,  it  will, 
however,  be  found  to  contain  at  least  one  million  bacteria  per  cubic 
centimeter;  and  if  these  bacteria  be  further  differentiated,  it  will  be 
found  that  most  of  them  are  of  a  harmless  type.     The  character  of 
sewage  is  naturally  extremely  variable,  depending  on  the  amount 
of  water  consumption  per  capita,  the  admission  of  storm  water 
into  the  system,  the  character  of  effluent  from  the  various  industries, 
and  the  constituents  of  the  mineral  compounds  in  the  water  supply 
itself.     It  will  also  vary  at  different  hours  of  the  day. 

113.  Analyses  of  Sewage.     Table  XIV  of  analyses  gives  an 
idea  of  the  composition  of  sewage.     It  will  be  noted  that  the  quan- 
tities are  expressed  in  parts  per  million  by  weight  and  that  a  com- 


SEWERS  AND  DRAINS 


137 


TABLE  XV 
Typical  Analysis  of  City  Sewage 


ANALYSIS    Or    ALLIANC£,0.   SEWAGE  JULY  1914 
Chester  &rieming     Consulting  Engineers    Pittsburgh,  Pa. 

| 
.S 

PARTS          PER          MILLION 

Ratio  of  Available  OxifQjen  to 
Oxijqen  Required  for  Equilib- 
rium Expressed  infer  Cent. 

STABILITY  at  37°  C. 

SUSPENDED  'SOLID 

DISSOLVED  OXYGEN 

CONSUMED  OXYGEN 

\ 

i 

]g 

1 

- 

I 

K^ 

^ 

1 

- 

§ 

s 

1 

Jo 

- 

V) 

I 

• 

f^ 

: 

'-- 

July  2 

257 

125 

69 

90 

0 

n 

n 

0 

45 

Z4.5 

29  2 

13.  d 

3 

Z.51 

190 

dO 

96 

0 

0 

0 

u 

b(J 

Jib 

36.4 

ld.0 

4 

£37 

193  ' 

105 

115 

I) 

n 

0 

0 

79 

lib 

27.6 

13.  b 

z 

0 

33 

yy 

5 

2  3d 

im 

36 

174 

06 

i) 

0 

0 

30 

&).() 

?8.0 

10.0 

99 

99 

6 

2  57 

16fi 

116 

136 

0 

0 

0 

1.7 

46 

Z5.0 

40.U 

7Tz 

7 

S  51 

195 

35 

103 

0 

0 

u 

l.b 

04 

'J6.0 

4Y.U 

Zb.Q 

8 

?4*i 

150 

7^ 

135 

o 

0 

0 

1  b 

49 

40.1) 

4Z.U 

lt.ti 

plete  detailed  analysis  of  the  constituent  parts  of  the  sewage  is 
not  made,  but  totals  of  the  solids,  organic  compounds,  and  other 
indicative  tests  are  given.  The  form  in  which  the  organic  matter 
exists  in  sewage  is  quite  complex  and  would  be  difficult  to  analyze, 
whereas,  indicative  tests,  which  can  be  used  for  comparison,  furnish 
the  information  desired. 

Table  XV  shows  an  analysis  of  sewage  and  effluents  from  the 
various  units  of  sewage  disposal  works  at  Alliance,  Ohio.  The 
significance  of  these  tests  is  as  follows: 

Suspended  Solids.  Dr.  Imhoff  divides  solids  found  in  sewage 
into  four  classes:  (1)  settling  solids  (removed  by  2  hours'  quiescent 
sedimentation);  (2)  finely  divided  solids  (finer  than  above  but 
removable  by  filtration  through  paper);  (3)  colloidal  matter  (finer 
than  either  of  the  above  but  removable  by  a  dialyzing  membrane) ; 
and  (4)  solids  in  true  solution. 

Of  these,  the  first  three  are  classified  as  suspended  solids  and 
are  subdivided  into  fixed  and  volatile  solids.  Most  of  the  fixed 
solids  represent  the  inorganic  matter  in  the  sewage,  consisting 
mainly  of  the  material  in  the  water  supply.  The  volatile  solids 
serve  as  an  index  of  the  amount  of  organic  matter  and  are  the  solids 
with  which  we  have  to  deal  in  purification. 

Nitrogen.  The  organic  nitrogen  indicates  the  amount  of 
undecayed  organic  matter  containing  nitrogen  in  the  sewage,  and 


138  SEWERS  AND  DRAINS 

the  free  ammonia  indicates  the  amount  of  decomposing  organic 
matter  containing  nitrogen.  The  nitrites  indicate  a  partial  break- 
ing down  of  the  organic  matter  into  inorganic  compounds,  and  the 
nitrates  indicate  the  amount  of  organic  matter  that  has  been  com- 
pletely broken  down  and  changed  into  stable  inorganic  compounds. 

Oxygen  Consumed.  A  very  important  test  as  indicating  the 
condition  of  the  sewage  with  respect  to  stability  shows  the  relative 
amount  of  carbonaceous  organic  matter  in  the  various  effluents. 
It  is  the  amount  of  oxygen  absorbed  by  the  sewage  and  is  used  to 
compare  with  the  effluent  as  to  purification  effected. 

Alkalinity.  The  alkaline  test  furnishes  a  comparison  of  the 
sewage  with  the  water  supply,  and  any  serious  modification  would 
indicate  pollution  with  trade  wastes  of  an  acid  character.  It  also 
serves  as  an  index  of  the  degree  of  purification  by  comparing  sewage 
with  effluent. 

Chlorine.  Chlorine  is  harmless  in  the  form  of  common  salt, 
in  which  it  occurs  in  sewage,  and  is  only  indicative  of  the  strength 
of  the  sewage. 

Bacteria.  Bacteria  are  microscopic  organisms  belonging  to 
the  vegetable  kingdom.  They  have  been  divided  into  two  classes, 
namely,  saprophytes,  which  live  on  inanimate  matter,  and  parasites 
which  live  on  substances  of  animal  bodies.  They  are  further  classi- 
fied by  their  ability  to  thrive  in  the  absence  or  presence  of  oxygen. 
Those  which  thrive  in  the  presence  of  oxygen  are  called  aerobic 
bacteria,  and  those  which  thrive  in  the  absence  of  oxygen  are  called 
anaerobic  bacteria.  Each  of  the  classes  has  so-called  facultative 
bacteria  also  which  exist  with  or  without  oxygen,  but  thrive  under 
the  conditions  suited  to  their  class.  Among  the  subdivisions  of 
these  general  classes  are  the  pathogenic  bacteria  which  are  the 
means  of  transmitting  water-borne  diseases.  These  bacteria  are 
of  course  parasites  and  do  not  increase  after  leaving  the  human 
body.  They  may  exist,  however,  for  months  under  most  unfavor- 
able conditions. 

The  reduction  of  organic  matter  to  inorganic  matter  is  accom- 
plished by  the  action  of  enormous  numbers  of  those  bacteria  upon 
the  organic  material.  It  has  been  found  from  experiments  and 
from  the  results  of  the  operations  of  numerous  biological  disposal 
plants,  that  aerobic  bacteria  in  the  presence  of  free  oxygen  bring 


SEWERS  AND  DRAINS 


139 


about  an  oxidizing  de- 
composition of  the  or- 
ganic matter  in  sewage 
with  but  few  or  no  objec- 
tionable  odors;  that 
anaerobic  bacterial  ac- 
tion, on  the  other  hand, 
in  the  absence  of  free 
oxygen  is  usually  accom- 
plished with  offensive 
odors  mainly  resulting 
from  sulphurated  hydro- 
gen compounds  which 
are  formed  thereby.  The 
total  number  of  bacteria 
in  the  sewage  per  cubic 
centimeter  is  indicative 
of  the  pollution,  and 
serves  as  a  comparison 
with  the  treated  sewage 
as  to  degree  of  purifica- 
tion. Where  disinfection 
of  the  sewage  is  desired, 
a  count  of  the  number  of 
b.  coli  communis  is  made. 
This  form  of  bacteria 
exists  in  the  intestines  of 
all  animal  life  and  is 
indicative  of  animal  pol- 
lution. While  it  is  in 
itself  harmless,  yet  it  is 
more  easy  to  differen- 
tiate than  the  pathogenic 
bacteria,  of  typhoid, 
cholera,  enteritis,  and 
other  water-borne  intes- 
tinal bacteria  which  may 
or  may  not  be  present, 


140  SEWERS  AND  DRAINS 

and  as  these  bacteria  are  less  hardy,  the  removal  of  b.  coll  is  an 
indication  of  the  removal  of  harmful  bacteria. 

DISPOSAL  SYSTEMS 

114.  Requirements  of  Sewage   Disposal.    The  requirements 
as  to  sewage  disposal  are  varied  for  there  are  few  cases  where  the 
conditions  are  the  same.     A  study  must  be  made  of  the  conditions 
in  each  particular  case,  taking  into  consideration  the  location  of 
water  supplies;  other  industries  which  might  be  affected;  the  capacity 
and  nature  of  the  stream  into  which  the  sewage  is  to  be  discharged; 
the  condition  of  the  sewage  itself;  the  possibilities  of  elimination 
of  storm  flows;  and  of  the  suitable  location  of  treatment  works.     The 
variation  of  the  hourly  flow  of  .the  sewage  must  also  be  studied 
where  treatment  works  are  to  be  installed  and  data  obtained  on 
the  amount  of  storm  water  admitted  during  rains. 

Fig.  43  shows  the  weekly  flow  of  the  sewage  at  Alliance,  Ohio. 
During  the  wet  season  this  flow  is  tripled  for  brief  periods. 

There  are  many  towns  on  large  bodies  of  water  where  dis- 
posal by  dilution  is  entirely  feasible.  On  smaller  streams,  a  partial 
purification  in  the  nature  of  the  elimination  of  solids  or  disinfection, 
or  both,  may  be  satisfactory,  and  in  other  cases,  on  small  streams 
or  in  locations  immediately  above  important  water  supplies,  the 
highest  degree  of  purification  must  be  effected,  including  the  removal 
of  all  organic  matter  and  the  disinfection  of  the  bacterial  content. 

115.  Classification  of  Methods.     The  methods  employed  in 
disposal   of  sewage  are  dilution   and  purification.     The  methods 
of  purification  now  in  use  consist  of  broad  irrigation,   chemical 
precipitation,  screens,  settling  tanks,  septic  tanks,   contact  beds, 
sprinkling  filters,   sand  filters,  disinfection,   and  electrolytic  treat- 
ment.    Each  of  these  methods  may  be  subdivided  into  various  types, 
but  in  this  book  it  is  the  intention  in  describing  them,  to  outline  only 
the  most  widely  used  and  successful  type  under  each.     In  considering 
the  different  methods,  it  is  to  be  understood  that  one  or  more  may 
be  necessary  to  solve  the  problem,  as  will  be  outlined  hereafter. 

DILUTION 

116.  Controlling  Factors.     Nearly  all  of  the  larger  cities  of 
America  dispose  of  their  sewage  by  dilution.     This  is  due  to  their 
location  on  the  seaboard  or  large  rivers. 


SEWERS  AND  DRAINS  141 

For  the  proper  dilution  of  sewage,  there  must  be  a  volume  of 
water  sufficient  to  permit  of  aerobic  bacterial  action  which  will 
effect  a  complete  breaking  down  of  the  organic  matter  and  at  the 
same  time  not  destroy  fish  life;  or  in  other  words,  the  oxygen  content 
of  the  stream  must  not  be  materially  reduced.  The  minimum 
is  set  by  authorities  at  from  30  per  cent  to  70  per  cent  of  the  satura- 
tion volume.  The  amount  of  water  required  to  attain  this  result 
depends  on  the  amount  of  dissolved  oxygen  in  the  stream  and  con- 
ditions for  replacing  it.  Leading  authorities  estimate  this  at  from 
4  cubic  feet  to  10  cubic  feet  per  second  per  1000  tributary  popula- 
tion. There  must  also  be  current  sufficient  to  prevent  silting-up 
of  the  stream  or  bay,  and  it  is  also  important  that  there  be  no  inshore 
currents  which  will  deposit  floating  material  on  the  shore  lines. 
Large  quantities  of  trade  wastes  from  industries  may  kill  fish  life 
and  must  therefore  be  considered.  The  distance  required  to  com- 
plete the  purification  by  this  method  varies  also  with  the  character 
of  the  stream.  A  mountain  stream  with  many  waterfalls  will 
manifestly  purify  itself  much  more  quickly  than  a  sluggish  lowland 
river.  There  are  no  signs  of  pollution  of  the  Mississippi  at  New 
Orleans  and  yet  it  receives  above  this  point,  the  sewage  of  over 
10,000,000  people.  However,  for  the  last  600  miles  it  travels 
through  delta  country  where  the  drainage  is  away  from  the  river. 

117.  Dilution  of  Chicago  Sewage.  The  Chicago  Drainage 
Canal  is  a  notable  example  of  disposal  by  dilution.  This  canal 
was  constructed  at  a  cost  of  $64,000,000  to  divert  the  flow  from 
the  lake  harbor  through  the  Chicago  River  to  the  Illinois  River, 
a  tributary  of  the  Mississippi.  The  sewage  is  diluted  on  a  basis 
of  3.3  cubic  feet  per  second  per  1000  population,  although  the  engi- 
neers in  charge  recommended  a  minimum  of  4  cubic  feet  per  second. 

The  Illinois  River  enters  the  Mississippi  357  miles  from  Chicago, 
a  few  miles  above  the  St.  Louis  Water  Works  Intake.  In  a  suit 
brought  by  the  city  of  St.  Louis  to  prohibit  this  arrangement, 
extensive  tests  showed  that  there  was  no  substantial  pollution  from 
this  source.  Recent  reports  show,  however,  that  for  a  distance  of 
one  hundred  miles  from  Chicago  along  the  Desplaines  and  Illinois 
rivers  there  is  a  very  unwholesome  condition  and  that  along  the 
Chicago  River  there  are  serious  nuisances.  Recommendations  have 
been  made  to  remove  the  solids  before  dilution. 


142  SEWERS  AND  DRAINS 

118.  Other  Examples  of  Dilution.    The  sewage  of  New  York 
is  discharged  through  many  outlets  into  New  York  Harbor.     This 
has  resulted  in  considerable  deposits  of  silt  at  many  points  and 
studies  are  now  being  made  of  a  partial  purification  of  sewage  from 
this  metropolitan  district. 

The  sewage  from  the  main  district  of  Boston  is  carried  by 
an  outfall  sewer  to  an  island  in  the  outer  harbor  where  it  is  stored 
in  basins  and  discharged  only  during  the  early  hours  of  the  out- 
flowing tide. 

Many  of  the  lake  cities  have  long  outlet  sewers  into  the  lake 
to  prevent  silting-up  and  deposit  of  solids  on  harbor  front,  and  also 
to  insure  proper  dilution. 

BROAD  IRRIGATION 

119.  General  Principles.     Broad  irrigation  is  the  oldest  type 
of  scientific  purification  of  sewage.     It   has  been   practiced  on  a 
large  scale  in  England  and  Germany,  and  several  installations  have 
been  made  in  America.     It  consists  in  applying  the  sewage  by  a 
system  of  ditches  to  farm  areas  with  the  idea  of  irrigating  them 
and  also  obtaining  the  fertilizing  value  of  the  sewage.     The  principle 
is  that  of  aerobic  bacterial  action  by  natural  filtration,  and  depends 
for  success  on  a  light  and  preferably  sandy  soil  and  on  being  able 
to  operate  uniformly  at  all  times  and  seasons  without  overloading 
the  treated  area.     An  acre  of  area  is  the  average  requirement  for 
each  one  hundred  of  tributary  population.     When  this  method 
first  came  into  use,  it  was  predicted  that  considerable  profit  would 
be  derived.     It  has,  however,  been  found  that  in  the  wet  seasons 
it  is  very  difficult  to  take  care  of  the  sewage  and  prevent  water- 
logging the  crops  without  by-passing  the  sewage;  and  that  as  a 
result  the  crops  that  can  be  raised  are  limited,  and  the  fertilizing 
value  of  the  sewage  does  not  justify  the  expense  required  to  apply 
it  properly. 

120.  Efficiency   of    Broad    Irrigation.     The   results   obtained 
from   well-operated   irrigation   farms   are   excellent.     The   effluent 
is  stable  with  a  marked  reduction  in  bacterial  count  and  in  many 
instances  showing  absence  of  b.  coli.     Dr.  Dunbar  states  that  he 
is  convinced  that  it  would  be  cheaper  for  many  towns  to  abandon 
irrigation  and  replace  it  with  artificial  biological  processes  and  that 


SEWERS  AND  DRAINS  143 

the  day  is  not  far  off  when  Berlin  will  sell  its  irrigation  farms  for 
building  purposes  and  construct  artificial  biological  filters. 

This  is  the  attitude  of  all  sanitary  engineers  at  the  present 
time.  The  only  condition  where  it  can  now  be  favorably  considered 
is  in  a  district  with  low  rainfall  where  irrigation  is  necessary  for 
crop  raising,  and  when  the  soil  is  adapted  to  irrigation. 

CHEMICAL  PRECIPITATION 

121.  Controlling   Factors.     The   method   of   sewage   disposal 
by  chemical  precipitation  was  introduced  by  various  private  com- 
panies under  patents  at  about  the  same  time  that  broad  irrigation 
came  into  use,  and  there  have  been  some  large  installations  in 
England,  Germany,  and  America. 

The  sewage  is  introduced  into  settling  tanks  where  it  is  treated 
with  chemicals  such  as  sulphate  of  iron  and  lime.  These  chemicals 
form  a  heavy  flocculent  precipitate  which  settles  in  the  tanks  and 
carries  with  it  a  part  of  the  suspended  matter  in  the  sewage.  The 
precipitated  material,  or  sludge,  is  then  drawn  off  and  usually 
compressed  by  sludge  presses  so  as  to  remove  the  water  and  facilitate 
handling. 

122.  Efficiency  of  Chemical  Precipitation.     It  has  been  found 
that  90  per  cent  of  the  total  suspended  matter  and  bacteria  can  be 
removed  from  sewage  by  this  process.     The  effluent  is  putrescible 
as  there  has  been  no  change  in  the  remaining  organic  matter. 

When  this  process  was  first  installed,  fabulous  claims  were 
made  of  the  value  of  the  sludge  as  fertilizers  from  plants  of  this  type. 
This  has  been  much  overrated  and  it  is  difficult  to  get  farmers 
to  come  to  the  plants  and  haul  it  free.  Many  such  plants  have  to 
deposit  the  sludge  in  fills  and  as  the  amount  will  average  5  cubic 
yards  per  million  gallons  of  sewage  treated,  there  is  a  considerable 
quantity  for  a  town  of  any  size.  The  high  cost  of  chemicals 
and  labor  required  in  the  operation  has  also  been  against  this 
method  which  is  no  longer  being  installed  for  municipal  disposal 
works. 

123.  Conditions  Favoring  Chemical  Precipitation.     There  are 
some  circumstances  in  dealing  with  trade  wastes  or  some  special 
conditions,  such  as  at  London,  under  which  the  chemical  process 
can  be  used  to  advantage. 


144  SEWERS  AND  DRAINS 

It  has  been  necessary  at  London  to  remove  the  suspended 
matter  to  prevent  the  silting  up  of  the  Thames.  This  has  been 
accomplished  by  treating  the  sewage  by  chemical  precipitation 
amounting  to  200,000,000  gallons  daily  in  nineteen  settling  tanks 
having  a  combined  capacity  of  44,000,000  gallons.  About  8,000 
cubic  yards  of  sludge  is  deposited  daily.  This  is  pumped  into 
tank  steamers  and  carried  out  to  sea. 

SCREENS 

124.  Purpose.     Coarse  screens  are  in  general  use  at  sewage 
pumping  stations  and  disposal  works  to  remove  the  coarse  suspended 
matters.     During  the  last  few  years,  mechanically   operated  fine 
screens  have  been  developed  in  Germany  which  can  remove  as 
high  as  80  per  cent  of  the  suspended  matter  from  the  sewage.     These 
fine  screens  are  now  being  introduced  into  America. 

125.  Coarse    Screens.    The   most   common   type   of   coarse 
screen  is  the  bar  screen  consisting  of  vertical  steel  bars  spaced 
from  \  inch  to  1  \  inches  apart  depending  on  conditions,  and  arranged 
in  a  masonry  pit  at  the  outlet  end  of  the  sewer  across  the  line  of 
flow  of  the  sewage.     The  fibrous  materials  in  the  sewage  make 
the  problem  of  cleaning  a  difficult  one  and  screens  must,  therefore, 
be  installed  in  duplicate  so  that  one  can  readily  be  removed.     For 
small   plants,  the   screens   are  usually  cleaned   by  the   attendant 
pulling  a  garden  rake  up  over  the  vertical  bars  several  times  daily. 
In  large  plants,  one  screen  is  removed  from  the  pit  by  hoists  or 
hydraulic  lift  and  cleaned  with  a  hose  on  the  operating  floor  above, 
or  some  form  of  mechanical  cleaning  device  is  used. 

The  material  obtained  from  coarse  screens  consists  of  rags, 
paper,  sticks,  lemon  peels,  and  other  coarse  organic  matter.  This 
is  usually  placed  in  large  cans  and  hauled  to  a  dumping  ground 
where  it  is  buried.  If  the  city  owns  an  incinerating  plant,  it  can 
be  mixed  with  the  garbage  and  burned. 

126.  Fine   Screens.     There  have   been  many   types   of  fine 
screens  developed,  with  varying  success.     The  best  known  type 
at  the  present  time  is  the  Reinsch-Wurl  screen  as  shown  in  Fig.  44. 
These  screens  consist  of  a  large  circular  plate  which  is  placed  at 
an  inclined  angle  in  the  outfall  sewer  and  is  revolved  about  its 
center.     This  plate  is  perforated  over  its  entire  surface  with  fine 


SEWERS  AND  DRAINS  145 

slots.     The  size  of  slot  and  diameter  of  plate  vary  with  the  amount 
of  sewage  to  be  treated  and  the  degree  of  purification  to  be  effected. 


Fig.  44.     Reinsch-Wurl  Screen  in  Experimental  Plant,  Dresden,  Germany 

As  the  plate  revolves,  the  deposited  solids  are  brought  above  the 
surface  of  the  sewage,  Fig.  45,  and  are  then  brushed  off  the  plate 


Fig.  45.     Reinsch-Wurl  Screen  in  Operation  at  Bremen ,  Showing   Brushes 

by  metallic  brushes  which  sweep  the  screenings  into  a  trough  where 
it  is  transported  to  the  sludge  presses  or  carted  away. 


146 


SEWERS  AND  DRAINS 


Fig.  46.     Installation  of  Reinsch-Wurl  Screens  at  Dresden,  Germany 


SEWERS  AND  DRAINS  147 

The  amount  of  power  required  to  drive  this  apparatus  is  small 
and  the  installation  is  much  less  expensive  than  settling  tanks. 
There  are  the  difficulties,  however,  of  a  higher  operating  cost  and 
the  problem  of  the  distribution  of  the  screenings.  The  screenings 
can  be  disposed  of  as  outlined  under  the  paragraphs  on  coarse 
screens,  but  on  account  of  their  amount,  it  is  preferable  to  make 
some  arrangement  regarding  their  use  as  fertilizers  with  the  farmers, 
who  will  take  them  free  unless  there  is  local  prejudice.  While 
these  screenings  have  some  value,  yet  they  must  be  removed  daily  and 
disposed  of  immediately  before  putrefaction  sets  in,  and  farmers  will 
not  agree  to  an  annual  contract  on  better  conditions  than  free  material, 
on  account  of  the  difficulty  of  distributing  it  in  winter  weather. 

The  plant  at  Dresden,  as  shown  in  Fig.  46,  is  the  largest  plant 
of  this  type  in  the  world.  It  was  installed  in  1911,  and  treats  a 
maximum  flow  of  4500  gallons  per  second.  For  three  months  in 
1911,  the  Elbe,  into  which  the  effluent  is  discharged,  had  a  flow 
of  less  than  one-half  that  of  the  incoming  sewage  and  yet  no  nuisance 
was  caused  thereby. 

These  fine  screen  installations  are  specially  adapted  to  use 
where  clarification  alone  is  required  for  conditions  under  which 
it  is  necessary  to  install  the  purification  works  adjacent  to  a  built-up 
district.  The  fresh  screenings  have  not  had  time  to  putrefy  and 
can  be  hauled  away  easily  without  offense.  They  are  also  used 
for  clarification  and  the  recovering  of  by-products  of  industrial 
waste,  and  under  special  conditions  for  screening  sewage  to  be  treated 

by  filters. 

SEDIMENTATION  TANKS 

127.  Efficiency.     The  method  generally  used    for  clarifying 
sewage    is    by    natural    sedimentation.      This    will    remove    from 
50  per  cent  to  75  per  cent  of  the  total  suspended  matter  from  the 
sewage  and  35  per  cent  of  the  organic  matter,  leaving  the  effluent 
with  the  balance  of  the  organic  matter  in  solution  and  in  suspension 
as  colloids.     Sedimentation  is  used  as  a  method  of  clarifying  sewage 
before  it  discharges  into  a  stream  where  dilution  is  feasible,  or  as 
the  first  step  in  complete  purification. 

128.  Classes.    There  are  three  general  classes  of  sedimentation 
tanks:  (1)  grit  chambers;  (2)  settling  tanks;  and  (3)  septic  tanks. 
These  classes  have  various  modifications  and  designs. 


148  SEWERS  AND  DRAINS 

129.  Velocity.     Practically  all  designs  are  based   on  a  con- 
tinuous flow  through  the  tanks  at  a  velocity  sufficiently  low  to 
deposit  the  suspended  matter.     Extensive  experiments  have  been 
made  to  determine  the  carrying  velocity  of  sewage-laden  water, 
and  as  a  result  of  these  experiments  authorities  place  the  maximum 
velocity  for  settling  tanks  at  one-half  inch  per  second,  and  the 
average  velocity  of  grit  chambers  at  1  foot  per  second. 

Grit  Chambers 

130.  Use.     Grit  chambers  are  used  on  combined  sewer  systems 
or  sanitary  systems  which  admit  some  street  drainage,  in  order 
to  remove  the  coarse  organic  suspended  matter  before  it  has  reached 
the  pumps  or  disposal  works.     Where  the   sewer   system    carries 
only  house  drainage,  they  are  unnecessary. 

131.  Design.    They  must   be  designed   so   that   no   organic 
matter  will  be  deposited  and  so  that  the  period  of  retention  is  not 
long  enough  to  start  septic  action.     A  velocity  of  1  foot  per  second 
will  deposit  the  grit  without  the  organic  matter  and  the  period 
of  retention  may  vary  from   a  few   seconds  to  5   or  10  minutes, 
depending  on  the  coarseness  of  the  material.     Where  the  amount 
of  sewage  varies  at  different  times,   several  compartments  must 
be  installed  with  automatic  overflow  weirs  so  that  the  velocity 
and  period  of  retention  may  be  uniform.     The  usual  design  is 
rectangular  in  plan  with  length  sufficient  to  give  the  required  period 
of  retention  and  velocity,  and  with  a  cross-section  suited  to  securing 
a  uniform  velocity  over  the  entire  area  without  complicated  baffling. 
The  bottom  should  be  sloped  on  a  10  per  cent  grade  to  an  outlet 
drain  controlled  by  a  valve.     The  details  of  design  are  very  similar 
to  those  for  the  more  complicated  settling  tanks,  which  will  be 
hereafter  described.     The  depth  used,  however,  is  comparatively 
shallow,  as  grit  chambers  must  be  cleaned  frequently,  and  too  much 
surplus  storage  capacity  would  affect  the  uniform  velocity  desired. 

Settling  Tanks 

132.  Settling  vs.  Septic  Tanks.     Settling  tanks  can  be  dis- 
tinguished from  septic  tanks  by  the  fact  that  putrefactive  action 
in  the  latter  results  from  the  action  of  anaerobic  bacteria  on  the 
organic  matter  retained  therein.     An  arbitrary  definition  of  septic 


SEWERS  AND  DRAINS  149 

tanks  has  been  that  they  must  have  an  uninterrupted  flow  without 
removal  of  sludge  for  at  least  six  weeks.  However,  newly  cleaned 
settling  tanks  have  shown  signs  of  septic  action  in  a  few  days  after 
being  placed  in  commission.  Settling  tanks  retaining  their  solids 
are,  however,  usually  distinguished  from  septic  tanks  by  the  frequent 
cleaning  periods  in  the  former  case,  and  the  six  weeks'  period  is 
usually  taken  as  the  dividing  line. 

133.  Basic  Conditions.     Settling  tanks  may  be  divided  into 
two  classes,  single-story  tanks  and  two-story  tanks.     The  govern- 
ing criteria  for  both  classes  are  a  maximum  velocity  of  one-half 
inch  per  second,  a  minimum  retention  period  of  one  hour,  and  a 
minimum  distance  of  horizontal  travel  of  35  feet. 

134.  Single=Story  Settling  Tanks.     Design.     The  usual  type 
of  the  single-story  settling  tank  is  rectangular  in  plan  and  has  a 
continuous  horizontal  flow  lengthwise  through  the  tank.     Several 
compartments  are  constructed  to  permit  one  or  more  tanks  to  be 
used  in  proportion  to  the  flow  of  sewage  and  to  permit  tanks  to  be 
cleaned  without  interfering  with  the  continuous  operation  of  the 
plant.     The  depth  of  tanks  should  preferably  be  12  feet  to  16  feet 
to  give  ample  room  for  storage  of  sludge  without  its  being  disturbed 
by  the  flow  of  sewage.     Their  capacity  should  be  a  retention  period 
of  from  1  hour  to  4  hours  with  additional  time  sufficient  for  sludge 
storage.     Their  length  and  width  are  governed  by  the  number  of 
units,  the  capacity  and  limitation  of  velocity  and  horizontal  travel 
given  above.     The  length  does  not  usually  exceed   100  feet  and 
the  width  is  usually  f  to  TV  the  length.     Covers  over  tanks  are 
not  necessary,  although  they  are  usually  installed  on  well-designed 
tanks  for  the  sake  of  appearance.     If  covers  are  used,  vents  must 
be  installed  for  gases.     It  is  important  to  obtain  a  uniform  distri- 
bution of  the  sewage  across  the  entire  cross-section  and  to  main- 
tain  a   uniform   velocity.     This   is   accomplished   by   distribution 
across  inlet  and  outlet  ends  and  by  one  or  more  baffles  across  the 
tanks.     It  is  very  necessary  to  design  the  tanks  so  that  they  can 
be  cleaned  easily.    The  bottoms  must  be  sloped  on  a  minimum 
slope  of  five  per  cent  to  a  central  sump  where  the  sludge  can  be 
drained  by  gravity  to  a  sludge  bed  or  can  be  pumped.     A  fire  hose 
with  water  under  good  pressure  is  indispensable  in  economic  clean- 
ing.   The  sludge  bed  must  be  constructed  of  gravel  or  other  porous 


150  SEWERS  AND  DRAINS 

material  and  be  well  underdrained.  The  minimum  depth  must 
be  at  least  12  inches,  and  the  surface  must  be  covered  with  a  mini- 
mum depth  of  2  inches  of  sand  to  retain  the  sludge.  The  sludge 
bed  must  be  of  area  sufficient  to  permit  the  sludge  to  be  deposited 
with  a  maximum  depth  of  six  inches  so  that  it  can  dry.  With 
this  depth  it  will  dry  under  favorable  conditions  in  from  one  to 
two  weeks.  With  well-digested  sludge,  an  area  of  0.3  square  feet 
per  inhabitant  is  sufficient. 

135.  Sludge.    The  sludge  problem  is  the  most  serious  one 
to  be  considered  with  settling  tanks.     If  they  are  frequently  cleaned, 
this  highly  putrescible  organic  matter  must  be  discharged  onto 
the  sludge  beds  every  few  weeks,  causing  very  disagreeable  odors; 
and  when  the  sludge  is  scraped  off  after  drying,  it  must  be  disposed 
of.     Where  the  number  of  tanks  is  sufficient  to  permit,  one  should 
be  placed  out  of  commission  so  that  the  sludge  can  digest  in  the 
tank  before  being  discharged,  as  a  period  of  several  months  is  required 
to  obtain  thorough  digestion.     This  is  accomplished  by  the  action 
of  anaerobic  bacteria,   which  usually  produce  offensive  gases  and 
cause  a  highly  septic  liquid  in  the  tank  above  the  sludge.     It  is 
therefore  dangerous  to  install  plants  of  this  type  within  half  a  mile 
of  residences. 

Septic  Tanks 

136.  Basic   Conditions.    These  tanks  are  the   same  as  the 
single-story  settling  tanks  previously  described,  except  that  septic 
action  or  the  action  of  anaerobic  bacteria  is  desired.     The  tanks 
are  designed  with  a  capacity  of  from  four  hours'  to  twenty-four 
hours'  settling  period  so  as  to  insure  capacity  enough  for  sludge 
storage.     In  America  the  maximum  is  twelve  hours.     The  flow 
through  the  tanks  is  continuous  and  at  a  slow  velocity,  exactly 
as  described  for  settling  tanks. 

As  the  sewage  flows  slowly  through  the  tank,  the  coarser  sus- 
pended matter  settles  to  the  bottom  where  it  is  attacked  by  millions 
of  anaerobes  which  have  developed  on  the  sludge  previously  retained. 
Lighter  particles  rise  to  the  surface  forming  a  thick  heavy  scum 
over  the  entire  surface.  Small  atoms  breaking  off  from  this  sink 
to  the  bottom,  while  light  ones  rise  from  below,  impelled  by  gases. 
All  these  are  teeming  with  anaerobes  which  are  liquefying  and  gasi- 


SEWERS  AND  DRAINS 


151 


fying  the  organic  matter. 
In  septic  tanks  sludge  is 
only  removed  when  there 
has  been  an  accumulation 
such  that  it  overtaxes  the 
sludge  capacity.  Where 
anaerobic  action  works  per- 
fectly, the  greater  propor- 
tion of  the  suspended  matter 
is  liquefied,  and  it  has  been 
found  that  after  retention 
for  three  or  four  months  the 
remaining  sludge  is  inodor- 
ous, while  in  many  cases  it 
is  removed  once  a  year  with 
little  or  no  nuisance.  The 
difficulties  experienced  with 
septic  tanks  are  from  the 
offensive  gases  usually  pres- 
ent in  the  tank  effluent. 
These  gases  are  liberated 
when  the  effluent  is  dis- 
charged onto  the  biological 
filters,  with  resulting  nui- 
sance to  adjacent  property. 
The  oxygen  content  of  the 
sewage  is  also  removed, 
which  places  it  in  bad  shape 
for  aerobic  treatment  either 
by  dilution  or  filtration. 

Where  septic  tanks 
wrork  perfectly  with  no 
attendant  odors  in  the 
effluent,  they  furnish  one  of 
the  best  methods  for  remov- 
ing the  suspended  matters. 
Most  of  the  single-story  set- 
tling tanks  in  America  are 


152  SEWERS  AND  DRAINS 

operated  as  modified  septic  tanks.  The  storage  capacity  of  the 
sludge  is  in  many  cases  limited,  requiring  frequent  removal  of  same, 
but  there  is  a  considerable  liquefaction  and  the  sludge  fairly  stable. 
It  is  difficult,  however,  to  prevent  fresh  sludge  that  has  just  been 
deposited  from  being  drawn  off  with  the  more  thoroughly  digested 
material  under  these  conditions. 

137.  Polk  Tanks.  Figs.  47  and  48  show  an  installation  of  set- 
tling tanks  of  this  type  which  are  used  to  remove  the  suspended 
matter  before  the  sewage  is  applied  to  sprinkling  filters.  Figs.  49 
and  50  show  the  details  of  these  tanks. 

This  plant  was  designed  to  purify  the  sewage  from  one  of  the 
largest  state  institutions  in  Pennsylvania,  and  to  discharge  it  into 


Fig.  48.     Covered  Settling  Tanks  of  Polk  Disposal  Plant 

a  small  stream  of  practically  pure  water  where  it  was  impossible 
to  obtain  a  flow  in  the  dry  season  sufficient  to  render  the  effluent 
from  the  sewers  inoffensive  or  properly  diluted.  The  plant  was 
designed  to  treat  daily  five  hundred  and  sixty-four  thousand  gal- 
lons. It  consists  of  screen  chambers,  settling  tanks,  sprinkling 
filters,  and  disinfection  apparatus,  for  the  disinfection  of  the  effluent 
with  chloride  of  lime. 

There  are  four  settling  tanks,  Fig.  48,  each  80  feet  long  by 
16  feet  wide  by  10  feet  deep,  and  each  with  a  capacity  of  96,000 
gallons,  which  permits  of  a  settling  period  of  12  hours  with  three 
tanks  in  operation. 

As  will  be  noted  in  Figs.  49  and  50,  the  sewage  is  admitted 
into  a  reinforced-concrete  distributing  trough  extending  across 


SEWERS  AND  DRAINS 


153 


the  inlet  ends  of  the  entire  group  of  tanks,  from  which  sewage  can 
be  admitted  into  one  or  more  compartments  through  two  or  thi;ee 


5PKrMKLIN(j        FILTERS 


T.K.  Inlet          ^Expansion  joint  throuqh 
Side  Walls  Only 


5ECTION-/1-B-C-D 


<•/£  Sludge  Line 

SECTION  E-F-G-H-U 

Fig.  49.     Detailed  Plan  and  Sections  of  Covered  Settling  Tanks 

gate  valves  located  immediately  below  the  flow  line.     A  distributing 
baffle  of  wood  is  constructed  across  the  inlet  end  of  each  tank  oppo- 


154 


SEWERS  AND  DRAINS 


site  these  gate  valves  at  a  distance  of  10  inches  from  the  wall  and 
extending  to  a  depth  of  2  feet  below  the  flow  line.  This  baffle 
distributes  the  sewage  uniformly  across  the  inlet  end  of  the  tank. 
At  the  outlet  end  of  each  tank  the  sewage  is  removed  over  a  steel 
weir  6  feet  long  located  at  the  flow  line  of  each  compartment  and 
at  the  center  of  the  wall.  This  weir  is  also  protected  by  a  wooden 


VIEW  SIDE  VIEW 

OF  INLET  Souti  BOARD 

Vent.  Pipe 


SECTION  MANHOLE  11 

6"5luice  Valve 


END  VIEW  SIDE  VIEW 

DETRIL  or  OUTLET  SCUMDOARD 


'Z"5lud<je  Line 

SECTION  SHOWING 
INLET  TO 


Fig.  50.     Diagram  Showing  Special  Details  of  Polk  Covered  Settling  Tanks 

baffle  to  assist  in  taking  off  the  sewage  uniformly  from  the  entire 
width  of  the  tank  and  to  protect  the  outlet  from  floating  material 
or  from  solid  matter  that  may  be  working  up  from  the  bottom 
of  the  tank  because  of  septic  action. 

A  movable  wooden  baffle  extending  4  feet  6  inches  below  the 
flow  line  is  suspended  on  a  trolley  running  the  length  of  the  tank 


SEWERS  AND  DRAINS  155 

and  can  be  located  at  any  point  between  the  inlet  and  outlet  ends 
as  may  be  desired.  This  baffle  is  also  used  to  prevent  cross-currents 
and  to  assist  in  a  uniform  flow  through  the  tank.  It  will  be  noted 
by  further  reference  to  the  illustrations  that  stop  planks  are  arranged 
on  the  outlets  of  the  various  compartments  and  on  the  inlet  and 
outlet  troughs  opposite  the  partition  walls  between  the  tanks. 
By  adjusting  these  stop  planks  the  tanks  can  be  operated  in  series 
instead  of  in  parallel. 

It  will  be  noted  that,  for  the  purpose  of  cleaning,  the  concrete 
bottom  of  each  compartment  slopes  on  a  5  per  cent  grade  to  a 
gutter  extending  lengthwise  through  the  center  of  each  tank,  as 
shown  in  section  GH  in  Fig.  49.  The  bottom  of  this  gutter  is  also 
placed  on  a  5  per  cent  slope  and  at  the  center  of  the  tank  there  is 
a  6-inch  valve  connection  for  draining  off  the  sludge  to  a  12-inch 
sludge  line,  extending  under  the  tanks  and  carrying  the  sludge 
by  gravity  to  sludge  beds.  It  will  also  be  noted  that  the  tanks 
are  covered  with  concrete  roofing  and  that  the  inlet  and  outlet 
troughs  are  covered  with  cast-iron  gratings  which  serve  to  improve 
the  general  appearance. 

This  plant  has  been  in  operation  for  over  five  years,  and  the 
results  obtained  from  these  settling  tanks  have  been  highly  satis- 
factory. They  have  maintained  uniformly  over  fifty  per  cent 
removal  of  the  suspended  matter  and  there  has  been  a  very  small 
accumulation  of  sludge,  most  of  it  being  liquefied  in  the  tanks. 
A  small  amount  is  removed  at  frequent  intervals  and  discharged 
on  the  sludge  bed  and  when  dried  is  scraped  off  and  plowed  into 
adjacent  ground.  There  have  been  no  complaints  of  offensive 
odors  and  practically  no  trouble  from  gases  liberated  by  anaerobic 
action.  The  plant  is,  however,  well  isolated,  being  three  thousand 
feet  from  the  institution.  It  is  typical  of  the  higher  grade  settling 
tanks  in  America  and  if  it  were  not  for  the  frequent  removal  of 
sludge,  thereby  preventing  complete  septic  action,  it  would  be 
typical  of  the  septic  tanks. 

138.  Two=Story  Tanks.  Basic  Conditions.  The  problem  of 
eliminating  the  nuisance  arising  from  the  use  of  settling  or  septic 
tanks  where  offensive  odors  are  in  many  cases  given  off  by  the 
effluents  due  to  the  anaerobic  action  in  the  compartments,  and  the 
difficulties  experienced  in  handling  the  sludge  and  obtaining  thorough 


156  SEWERS  AND  DRAINS 

digestion  of  it  before  it  is  removed  from  the  tanks,  has  resulted 
in  the  development  of  a  type  of  tank  where  the  sewage  flowing 
through  the  tank  is  kept  entirely  separate  from  the  deposited  sus- 
pended matters.  It  has  been  found  also  that  septic  action  does 
not  benefit  the  liquids  for  the  secondary  treatment  on  the  biological 
filters,  but  that  in  fact  it  is  preferable  to  get  the  liquids  to  the  bio- 
logical filters  in  a  condition  as  fresh  as  possible,  in  order  to  retain 
some  oxygen  which  would  be  favorable  in  the  secondary  treatment. 
The  typical  tank  of  this  type  is  the  Imhoff  tank  developed  by  Dr. 
Karl  Imhoff,  the  German  expert. 

Design.    In  this  type  of  tank  the  sewage  flows  through  an 
upper    compartment    under    the    conditions    previously    specified 


Fig.  51.     Installation  of  Imhoff  Tanks  at  Atlanta,  Georgia 

for  travel  and  velocity,  but  with  a  retention  period  of  from  one  to 
four  hours.  The  compartment  is  equipped  with  a  sloping  bottom 
placed  on  a  slope  of  not  less  than  1.2  vertical  to  1  horizontal,  and 
terminating  in  a  sealed  slot,  with  a  lap  horizontally  of  at  least 
8  inches.  This  slot  discharges  into  a  lower  compartment  that  has 
no  connection  with  the  upper  compartment  other  than  the  sealed 
slot.  This  lower  compartment  is  designed  to  retain  a  capacity 
of  at  least  'six  months'  sludge,  based  on  a  capacity  of  1000  cubic 
feet  per  thousand  inhabitants.  The  lower  compartment  is  usually 
built  cone  shape,  terminating  in  a  sump  at  the  bottom  from  which 
there  is  a  discharge  line  for  the  sludge  bed.  There  must  also  be 
an  opening  from  the  compartment  to  the  surface  as  a  discharge 
for  gases  and  as  an  admission  for  cleaning.  As  the  sludge  is  drawn 


SEWERS  AND  DRAINS 


157 


from  the  bottom  of  the  compartment,  and  as  there  is  six  months' 
capacity  for  anaerobic  action,  if  the  sludge  is  drawn  off  in  small 


Fig.  52.     Interior  View  of  Imhoff  Tanks  at  Batavia,  New  York 


Fig.  53.     Installation  of  Imhoff  Tanks  at  Essen,  North  Germany 

quantities  at  intervals  of  six  weeks,  only  thoroughly  worked  over 
sludge  will  be  placed  on  the  sludge  beds  and  the  result  is  that  there 
can  be  no  nuisance. 


158 


SEWERS  AND  DRAINS 


SEWERS  AND  DRAINS  159 

Operating  Results.  Figs.  51  to  53  show  installations  of  this 
type  of  tank  at  Atlanta,  Georgia,  Fig.  51;  at  Batavia,  New  York, 
Fig.  52;  and  at  Essen,  North  Germany,  Fig.  53.  The  Atlanta  plant 
was  placed  in  service  in  1912,  and  the  result  of  the  operations  for 
the  years  1913  and  1914,  which  was  recently  published,  showed 
an  average  removal  of  total  suspended  matter  by  the  Imhoff  tanks 
of  80  per  cent.  The  average  period  of  retention  in  the  flow  of 
sewage  was  two  hours.  The  plant  at  Batavia,  New  York,  which 
was  installed  in  1912,  is  also  giving  excellent  results.  No  nuisance 
has  been  noticed  at  either  plant  and  the  sludge  removed  from  the 
tanks  has  been  well-digested  and  inodorous. 

139.  Greenville  Tanks.  There  are  various  forms  of  design 
for  the  Imhoff  tanks.  Fig.  54  shows  the  plans  for  the  Imhoff  tanks 
to  be  installed  for  Greenville,  Pennsylvania.  These  tanks  are 
of  the  circular  type,  constructed  in  pairs  and  arranged  for  a  longi- 
tudinal flow  through  each  pair.  Piping  facilities  provide  for  revers- 
ing this  flow,  a  necessary  operation  every  few  weeks  in  order  that 
the  deposited  material  may  be  uniformly  distributed  in  both  tanks. 
The  entire  capacity  of  this  plant  is  one  million  gallons  per  24  hours 
based  on  a  settling  period  of  1|  hours,  and  on  a  sludge  storage  of 
6  months  for  seven  thousand  people.  Imhoff  tanks  are  constructed 
of  reinforced  concrete  and  the  arrangement  for  admitting  sewage 
to  the  tanks  and  reversing  its  flow  is  by  means  of  cast-iron  pipe 
lines  controlled  by  concrete  manholes  with  stop  planks  as  shown. 
Sewage  is  distributed  across  the  inlet  end  of  the  tank  by  concrete 
weirs  spaced  uniformly  along  the  outer  edge  of  a  trough  of  the 
same  material  built  across  the  entire  width  of  the  tank  at  the  inlet  end 
and  protected  by  a  wooden  baffle  extending  to  a  depth  of  24  inches 
below  the  flow  line.  This  baffle  serves  to  distribute  sewage  uni- 
formly across  the  entire  tank.  Sewage  is  taken  off  at  the  opposite 
end  of  the  pair  of  tanks  by  a  concrete  trough  similar  to  the  one 
described,  also  protected  by  a  skimming  baffle.  The  upper  com- 
partment is  separated  from  the  lower  compartment  by  a  reinforced- 
concrete  slab,  terminating  in  two  slots  on  each  side  of  a  wedge 
frame  built  at  the  bottom  of  the  compartment  as  shown.  (See 
section  BB  of  Fig.  54.)  It  will  be  noted  in  the  design,  that  the 
upper  or  settling  compartment  is  common  to  the  two  tanks,  but 
that  the  lower  or  sludge  compartments  are  entirely  independent 


160 


SEWERS  AND  DRAINS 


of  each  other.  The  sludge  is  removed  from  a  sump  at  the  center 
of  the  sludge  compartment  of  each  tank  by  means  of  an  8-inch 
sludge  pipe  extending  to  within  a  few  feet  of  the  flow  line  of  the 
tank,  where  it  is  connected  by  a  valve  to  a  gravity  drain  extending 


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Fig.  55.     Plan  of  Sewage  Disposal  Plant  at  Connellsville,  Pennsylvania 

to  the  sludge  bed.  Without  interfering  with  the  operation  of  the 
tank,  sludge  is  removed  by  hydraulic  pressure  in  the  tank  upon 
opening  this  valve.  It  will  be  further  noted  by  reference  to  the 
illustration  that  ample  area  is  left  along  the  sides  of  the  settling 


SEWERS  AND  DRAINS 


161 


compartment  at  the  top  of  the 
Imhoff  tanks  for  ventilating  the 
lower  compartment.  These  com- 
partments are  covered  with  remov- 
able wooden  gratings  as  shown. 

140.  Radial=Flow  Tanks. 
Figs.  55  and  56  show  a  typical 
design  of  what  is  known  as  the 
radial-flow  Imhoff  tanks.  These 
tanks  were  designed  for  a  sewage 
disposal  plant  for  Connellsville, 
Pennsylvania,  a  town  having  a 
population  of  sixteen  thousand  and 
a  flow  of  sewage  of  three  million 
gallons  per  24  hours.  Two  radial- 
flow  Imhoff  tanks  are  planned  for 
this  installation.  They  are  designed 
for  two  hours'  capacity  in  the  set- 
tling compartment  and  for  a  six 
months'  storage  of  sludge,  and  are 
to  be  constructed  of  reinforced  con- 
crete. Sewage  will  be  admitted 
through  a  manhole  between  the 
tanks,  Fig.  55,  from  which  it  will  be 
diverted  to  one  or  both  of  the  tanks 
by  means  of  stop  planks  controlling 
20-inch  cast-iron  pipes  extending  to 
the  circular  trough  near  the  center 
of  each  tank.  This  circular  trough 
will  be  14  feet  in  diameter  and  27 
inches  wide,  and  will  have  slots  in 
the  bottom  of  it  spaced  uniformly 
around  the  circumference  at  a  depth 
of  3  feet  below  the  flow  line.  The 
diameter  of  each  tank  will  be  58  feet. 
The  settling  chamber  will  be  sepa- 
rated from  the  sludge  chamber  by 
a  cone  diaphragm  of  concrete  as 


162  SEWERS  AND  DRAINS 

shown,  with  a  slot  located  at  the  bottom  of  the  diaphragm,  between 
it  and  the  outside  sloping  wall  of  the  tank.  Halfway  across  the 
settling  chamber  between  the  circular  inlet  and  outlet  troughs, 
there  will  be  a  concrete  baffle  extending  to  a  depth  of  half  the  tank 
at  this  point  from  the  top.  The  outlet  trough  will  be  arranged 
with  outlet  weirs  spaced  along  the  top  of  the  trough  at  uniform 
distances  and  at  the  same  level.  The  sludge  compartment  will  be 
drained  by  a  sludge  pipe  extending  from  a  sump  at  the  center 
of  the  compartment  to  a  gate  valve  located  outside  of  the  tank 
and  5  feet  below  the  flow  line.  By  opening  this  valve  the  sludge 
will  be  drained  by  hydraulic  pressure  without  interfering  with  the 
operation  of  the  tank. 

Flushing.  One  of  the  most  important  adjuncts  to  equipping 
Imhoff  tanks  is  a  good  fire  hose  with  plenty  of  water  pressure,  and 
with  facilities  for  applying  it  to  any  portion  of  the  tanks.  This 
is  valuable  in  breaking  up  or  removing  any  scum  formation  in 
the  settling  compartment,  in  keeping  the  sludge  pipe  clean,  and  in 
washing  off  any  compartment  which  may  be  drained. 

CONTACT  BEDS 

141.  Use.     Contact  beds  are  a  type  of  the  biological  filters 
generally  used  for  treating  sewage  from  which  most  of  the  suspended 
matter  has  been  removed  by  sedimentation  or  by   fine  screens. 
They  are  employed  to  further  remove  additional  organic  and  sus- 
pended matter  and  to  render  the  effluent  non-putrescible. 

142.  Basic   Conditions.     Contact   filters   are   constructed   of 
broken  stone,  hard  slag,  or  well-burned  cinders,  preferably  of  material 
ranging  in  size  from  J  inch  to  2  inches.     The  filters  are  usually 
of  an  effective  depth  of  from  1  foot  to  5  feet,  depending  on  the 
amount  of  head  available.     The  best  depth  is  4  feet  to  5  feet  and 
with  this  depth  a  maximum  flow  of  700,000  gallons  of  clarified 
sewage  can  be  treated  per  acre.    As  a  general  rule  150,000  gallons 
per  acre  is  the  maximum  amount  that  can  be  treated  for  each  foot 
of  filter  depth.     The  beds  must  be  operated  so  that  they  will  be 
frequently  filled  with  air,  as  the  action  is  entirely  that  of  aerobic 
bacteria.    These   bacteria   exist   in   enormous   numbers   over   the 
surface  of  the  filtering  material  throughout  its  entire  depth.     When 
the  sewage  is  placed  in  contact  with  this  filtering  material,  the  remain- 


SEWERS  AND  DRAINS  163 

ing  suspended  matter  in  the  sewage  consisting  mainly  of  colloids 
and  non-settling  solids,  is  to  a  great  extent  retained  in  contact 
with  the  filtering  material  by  attrition;  and  the  enormous  bacterial 
growths  of  aerobic  bacteria  attack  this  organic  matter,  quickly 
reducing  it  to  inorganic  forms. 

143.  Design.    Most  of  the  contact  filters  installed  in  America 
are   operated   on   the  fill-and-draw  method,   being   controlled   by 
automatic  apparatus  which  admits  the  sewage  to  one  unit  of  a 
group  of  filters  and  when  this  is  full  opens  up  the  outlet  from  it, 
and  at  the  same  time  starts  the  sewage  flowing  into  the  next  filter. 
These  filters   must  be  constructed   as  water-tight  compartments 
and  are  usually  built  of  concrete.     The  number  of  groups  to  be 
used  and  the  size  of  units  in  each  group  depend  upon  the  amount 
of  sewage  to  be  handled  and  the  depth  of  filter  desired.     It  is  usually 
not  desirable  to  .have  the  units  larger  than  a  quarter  of  an  acre 
each,  and,  on  the  other  hand,  it  is  advisable  to  have  at  least  four 
units  in  order  to  secure  long  resting  periods  between  the  dosing. 
It  has  been  found  that  the  period  of  retention  has  very  little  to 
do  with  the  efficiency,  so  that  in  most  installations,  the  apparatus 
is  arranged  in  such  a  way  that  the  tank  starts  to  empty  a  few  min- 
utes after  it  has  filled. 

144.  Alliance  Filters.     Figs.  57,  58,  and  59  show  a  plan  of 
the  plant  and  the  contact  filters  of  Alliance,  Ohio,  and  the  auto- 
matic control  apparatus  for  one  group. 

As  will  be  noted  upon  reference  to  the  plans,  the  Alliance  filters 
are  designed  to  treat  sewage  clarified  by  settling  tanks.  They 
have  a  capacity  for  two  million  gallons  of  sewage  per  day.  They 
consist  of  three  groups,  each  with  a  total  area  of  one  acre  and  sub- 
divided into  four  filters.  Each  filter  has  an  effective  depth  of  5 
feet  and  consists  of  a  concrete  compartment  filled  with  well-burned 
cinders  and  underlaid  by  tile  drains  upon  the  floor,  which  drain 
to  the  central  control  chamber.  The  sewage  flows  from  the  settling 
tanks  to  the  central  control  chamber  of  each  group  of  contact  beds, 
where  it  is  distributed  by  automatic  air-lock  apparatus  on  to  each 
bed  at  the  surface.  This  apparatus  consists  of  Miller-Adams 
siphons,  each  of  which  is  controlled  by  an  air  bell  which  can  break 
the  siphon  seals.  These  air  bells  are  located  in  concrete  compart- 
ments and  connected  by  small  pipes  to  the  siphons.  As  the  water 


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SEWERS  AND  DRAINS 
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166  SEWERS  AND  DRAINS 

rises  in  these  compartments  which  are  connected  up  to  the  filters, 
it  displaces  the  air  in  the  bells,  gradually  compressing  it  until  it 
is  of  pressure  sufficient  to  displace  the  sewage  in  the  connected 
siphon,  so  that  when  one  filter  is  full,  it  closes  itself,  opens  up  the 
inlet  valve  to  another  filter,  and  then  opens  up  the  outlet  valve 
of  the  filter  just  filled. 

145.  Head  Required.  Contact  filters  are  well  adapted  to 
gravity  filtration  plants  where  the  loss  of  head  due  to  the  operation 
of  the  plant  is  limited  to  6  feet  or  8  feet.  They  are  much  more 
expensive  in  construction  than  sprinkling  filters,  which  are  less 


Fig.  59.     Automatic  Control  Chamber  for  Contact  Beds  at  Alliance,  Ohio 

likely  to  clog  up  and  which  give  equally  good  results.     Sprinkling 
filters,  however,  require  at  least  eleven  feet  of  head. 

SPRINKLING  FILTERS 

146.  Use.     Sprinkling  filters  operate  on  the  same  principle 
as  contact  filters  and  are  used  for  the  same  purpose,  although  the 
method  of  application  of  the  clarified  sewage  is  entirely  different. 
They  are  essentially  biological  filters  depending  upon  the  action 
of  aerobic  bacteria,  and  the  same  method  of  removing  the  remaining 
suspended  and  organic  matter  from  the  sewage  is  carried  out  in 
the  sprinkling  filters. 

147.  Design.     Sprinkling  filters   do   not   require   water-tight 
concrete  compartments  and  do  not  have  to  be  subdivided.     They 
can,  therefore,  be  constructed  much  more  cheaply  than  contact 
beds.    They  are  built  with  an  effective  depth  of  from  5  feet  to  8 


168 


SEWERS  AND  DRAINS 


feet  and  are  constructed  of  broken  ,stone  or  other  material  with  a 
dense  clear  fractured  surface  of  a  size  ranging  from  1  inch  to  3 
inches.  The  sewage  is  applied  to  the  surface  every  fifteen  or  twenty 
minutes  by  means  of  troughs,  nozzles,  or  traveling  distributors 
so  as  to  spread  uniformly  in  a  fine  spray  over  the  entire  surface, 
Fig.  60.  It  then  trickles  down  through  the  broken  stone,  only 
a  few  minutes  being  required  for  it  to  pass  through  the  filters.  The 
period  of  application  is  usually  five  minutes.  The  bottom  of  the 
filter  is  entirely  underlaid  with  tile  to  assist  in  aeration,  and  provision 
is  usually  made  for  ready  access  to  the  underdrains  and  distributors, 
for  frequent  inspection  and  for  cleaning  if  necessary. 

Sprinkling    filters    are    operated    in    America    under    ordinary 
conditions  with  clarified  sewage  at  a  rate  of  two  and  one-half  million 


Fig.  61.     Danville,  Pennsylvania,  Sprinkling  Filters  in  Operation  at  14  Degrees  below  Zero 

gallons  per  acre  per  day.  Here  the  usual  method  of  distributing 
the  sewage  on  to  sprinkling  filters  is  by  fixed  nozzles  connected 
by  piping  system  to  an  automatic  siphon,  or  to  a  motor-driven 
rotating  valve.  This  siphon  or  valve  is  supplied  by  a  dosing  tank 
of  capacity  sufficient  to  furnish  a  five-minute  dose  to  the  filter 
and  permit  the  desired  resting  period.  These  tanks  are  usually 
built  in  the  form  of  an  inverted  cone  and  are  known  as  tapered 
tanks,  this  arrangement  being  necessary  to  distribute  uniformly 
the  sewage  over  the  area  supplied  by  each  fixed  nozzle.  The  flow 
line  in  this  tank  is  from  5  feet  to  10  feet  above  the  surface  of  the 
filter  in  order  to  give  the  pressure  necessary  for  distribution.  It 
is,  therefore,  essential  to  have  a  total  head  of  at  least  11  feet  for 
proper  operation  of  sprinkling  filters  with  fixed  nozzles. 


SEWERS  AND  DRAINS 


169 


170 


SEWERS  AND  DRAINS 


148.  Results.     The  effluent  from  filters  of  this  type  is  more 
putrescible  and  usually  shows  a  marked   reduction   in   bacterial 
count  over  the  raw  sewage.     These  filters  are  self-cleansing,  freeing 
themselves  of  the  accumulated  material  after  it  has  been  mineral- 
ized.   The  effluents  are,  therefore,  not  clear,  but  this  suspended 
material  may  be  removed  by  settling. 

149.  Examples.     Figs.    60    and    61    show    sprinkling    filters 
in  operation  for  the  Polk  Plant  and  the  Danville  Plant.     The  Dan- 
ville filters  were  being  operated  at  a  temperature  of  fourteen  degrees 


Fig.  63.     Interior  of  Small  Sprinkling  Filters,  Showing  Distribution  System 

below  zero  at  the  time  this  picture  was  taken.  No  trouble  has 
been  experienced  in  America  in  operating  sprinkling  filters  during 
cold  weather. 

150.  Polk  Filters.  Figs.  62,  63,  and  64  show  details  of  the 
construction  of  sprinkling  filters.  It  will  be  noted  that  all  of  the 
filters  are  operated  by  automatic  siphons  supplied  by  concrete  tanks 
at  the  outlet  ends  of  the  settling  tank.  These  siphon  chambers  are 
designed  for  a  capacity  sufficient  to  give  an  interval  of  fifteen  to 
twenty-five  minutes  between  doses  as  may  be  desired. 


SEWERS  AND  DRAINS 


171 


To  refer  in  detail  to  the  Polk  sprinkling  filters,  which  are  typical 
of  American  installations,  these  filters  are  designed  in  two  units, 
separated  by  a  concrete  gallery  in  which  are  located  the  valving 
and  connections  for  the  distributing  line.  This  gallery  is  4  feet 
wide  and  6  feet  deep.  Under  the  floor  of  this  gallery  there  is  an 
18-inch  conduit  connected  to  the  siphon  chamber  at  one  end  of 
the  gallery  and  adjacent  to  settling  tanks.  From  this  conduit 


Fig.  64.     Interior  of  Sprinkling  Filter,  Showing  Underdrains  Partly  Laid 

at  intervals  of  12  feet  there  are  6-inch  risers  which  supply  the  4-inch 
distributing  lines  in  the  two  filters.  Each  distributing  line  is  con- 
trolled by  a  4-inch  valve.  The  distributing  lines,  as  will  be  noted, 
are  constructed  of  cast  iron  and  are  supported  every  twelve  feet 
by  concrete  columns.  Along  these  distributing  lines  are  located 
the  riser  pipes  to  the  nozzles,  which  are  so  spaced  as  to  place  the 
nozzles  14  feet  center  to  center.  The  distributing  lines  can  be 


172 


SEWERS  AND  DRAINS 


Note-  Detail  of  Riser  Cop  is  at 
One-Half  the  Scale  of  De- 
tail of  Sprinkling  Nozzle. 


cleaned  readily  by  removing  the  flanged  elbows  in  the  operating 
gallery.  The  nozzles  consist  of  a  brass  throat  T\  inch  in  diameter, 
above  which  is  set  a  brass  cone,  as  shown  in  Fig.  65.  The  sewage 
when  discharged  through  the  throat  of  the  nozzle,  strikes  this  cone 
and  is  sprayed  over  the  surface  of  the  filter  as  indicated  in  the 
illustration.  The  underdrains  for  these  filters  consist  of  6-inch 
split  tile  laid  on  a  concrete  slab  and  sloping  from  the  control  gallery 
to  a  cross-drain  located  at  the  opposite  side  of  each  filter.  These 
underdrains  are  spaced  12  inches  center  to  center  and  extend  through 

the  gallery  wall  to  the  in- 
terior so  that  they  can  be 
flushed  out  with  a  hose  from 
the  gallery  and  can  also  be 
ventilated  through  same. 
The  filtering  material  con- 
sists of  a  hard  sandstone 
ranging  in-size  from  4  inches 
to  1  inch  with  an  effective 
depth  of  6  feet.  These 
filters  are  constructed  with 
concrete  walls  around  each 
unit.  In  many  installa- 
tions, however,  a  dry  rubble 
wall  is  used  for  the  outside 
•  walls  and  in  some  cases 
where  the  filters  are  located 

above  ground,  the  filtering  material  itself  is  carefully  laid  up  to 
serve  as  a  wall  for  the  filter. 

SAND  FILTERS 

151.  Use.  Sand  filters  represent  an  artificial  type  of  broad 
irrigation  in  two  respects:  (1)  they  consist  of  specially  prepared 
filters  of  coarse  sand,  well  underdrained  and  provided  with  dis- 
tributing troughs  for  applying  the  sewage  uniformly  to  the  surface; 
and  (2)  the  results  obtained  are  from  the  action  of  aerobic  bacteria 
on  the  organic  and  suspended  matter  that  is  retained  in  the  sand. 
They  may  be  used  to  treat  raw  sewage  or  clarified  sewage  or  as 
a  final  treatment  after  biological  filters.  Sand  filters  will  give  a 


DETAIL  OF  SPRINKLING  NOZZLE 
Fig.  65.     Details  of  Sprinkling  Filter  Nozzle 


SEWERS  AND  DRAINS  173 

much  higher  degree  of  efficiency  than  the  two  types  of  biological 
filters  previously  described,  and  the  effluent  from  sand  filters  should 
not  only  show  a  high  degree  of  efficiency  in  the  removal  of  organic 
matter,  but  also  a  marked  reduction  in  the  bacteria. 

152.  Design.     Sand  filters  require  an  area  of  1J  acres  per 
1000  people  for  raw  sewage;  J  to  1  acre  per  1000  people  for  clarified 
sewage;  and  J  to  J  acre  per  1000  people  as  a  final  for  biological 
filters.     They  must  be  operated  intermittently  to  permit  a  thorough 
aeration  of  the  sand  between  the  treatment  periods.     These  filters 
are  usually  constructed  of  a  depth  of  from  2  feet  to  4  feet  and  are 
underlaid  with  underdrains  in  a  manner  similar  to  the  contact 
filters.     The  sewage  is  usually  applied  to  a  depth  of  2  inches  over 
the  entire  surface  of  the  filter  at  intervals  of  not  less  than  8  hours 
apart  and  at  longer  intervals  if  possible.     The  sewage  is  usually 
distributed  by  a  series  of  wooden  troughs  extending  over  the  surface 
of  the  filter  from  the  automatic  control  apparatus  and  provided 
at  frequent  intervals  with  gates  or  notches  for  spreading  the  sewage 
over  the  surface.     In  cold  climates  a  ridge  and  furrow  method 
of  distribution  must  be  used  to  prevent  freezing. 

Sand  filters  are  usually  installed  in  groups,  arranged  and  con- 
trolled in  a  manner  similar  to  that  described  for  contact  beds, 
with  the  exception  that  the  sewage  is  applied  to  the  trough  system 
on  the  surface,  there  being  no  control  to  the  outlet  drains. 

153.  Alliance    Filters.     Fig.    66    shows   the   arrangement    of 
sand  filters  which  are  used  to  filter  the  effluent  from  the  contact 
beds  at  Alliance,  Ohio.     Sewage  is  allowed  to  run  onto  one  bed  at 
a  time  from  a  common  collector  connected  with  the  contact  beds. 
After  several  hours,  the  flow  is  shut  off  by  hand  and  turned  onto  the 
next  bed.   These  beds,  with  a  uniform  depth  of  three  feet,  have  a  total 
area  of  four  acres  and  are  therefore  designed  to  treat  the  contact 
bed  effluent  at  a  rate  of  500,000  gallons  per  acre  per  day.     Having 
been  distributed  over  the  surface  by  wooden  troughs,  the  sewage  is 
collected  by  a  system  of  terra  cotta  tile  drains  as  shown.     A  central 
control  tank  is  also  frequently  installed  of  a  capacity  sufficient 
to  dose  out  enough  sewage  to  cover  the  surface  of  the  filter  to  a 
depth  of  2  inches  and  to  store  enough  to  give  the  proper  periods 
of  intermission,  as  above  outlined. 

Sand  filters  in  most  locations  in  America  call  for  an  installation 


174 


SEWERS  AND  DRAINS 


expensive  in  comparison  with  that  of  contact  beds  or  sprinkling 
filters  supplemented  by  disinfection,  and  they  are  therefore  few 


Fig.  66.     Plan  of  Sand  Filters  at  Alliance,  Ohio 


in  number  on  any  scale,  outside  of  the  New  England  district  where 
sandy  areas  are  abundant. 


SEWERS  AND  DRAINS  175 

DISINFECTION 

154.  Purpose.    Where  sewage  or  the  effluent  from  a  disposal 
plant  is  discharged  into  a  stream  above  a  water  supply,  it  is  neces- 
sary to  remove  the  danger  of  transmitting  water-borne  diseases. 
This  is  accomplished  by  disinfection  or  the  removal  of  pathogenic 
bacteria  as  indicated  by  the  absence  of  b.  coli.     Sterilization  con- 
sists in  the  removal  of  all  bacteria.     As  the  pathogenic  bacteria 
are  weaker  than  the  rest  of  the  sewage  bacteria,  they  are  removed 
more  easily  and  at  less  expense.     It  is  found  also  that  in  sterilizing 
sewage,  the  organic  matter  is  unaffected  and  upon  its  being  dis- 
charged into  a  stream,  new  growths  of  bacteria  will  quickly  develop 
from  those  already  in  the  stream.     Sterilization  is,  therefore,  usually 
not  attempted. 

155.  Method.     Disinfection    may    be    accomplished    by    the 
application  of  a  definite  amount  of  hypochloride  of  lime  in  solution, 
or  chlorine  gas,  or  electrolytic  action.     Chloride  of  lime  may  be 
purchased  commercially  at  from  1J  cents  to  3  cents  per  pound 
depending  on  the  size  of  containers,  with  a  rated  strength  of  33 
per  cent  available  chlorine.     It  is  then  dissolved  in  a  weak  solution 
of  water,  and  this  solution  is  applied  to  the  sewage  at  a  rate  of  3 
to  4  parts  available  chlorine  per  million  parts  of  sewage  by  weight, 
or  75  to  100  pounds  per  million  gallons.     At  this  rate,  a  complete 
removal  of  b.  coli  can  be  obtained  and  a  great  reduction  in  total 
bacteria.    Most  of  the  bacteria  are  destroyed  instantly,   but  it 
is  necessary  to  have  fifteen  or  twenty  minutes'  contact  to  obtain 
thorough  disinfection.     After  treatment,   the  sewage  is  therefore 
allowed  to  flow  through  a  compartment  of  fifteen  or  twenty  minutes' 
maximum  flow  capacity. 

The  chlorine  gas  treatment  costs  about  the  same  as  the  chloride 
of  lime  and  is  more  efficient  in  that  it  is  more  easily  controlled. 
It  consists  of  containers  of  chlorine  gas  compressed  to  a  liquid. 
This  liquid  is  fed  by  automatic  apparatus  at  the  desired  rate  into 
the  sewage. 

The  electrolytic  treatment  is  more  expensive  in  operation 
under  ordinary  conditions.  It  consists  in  passing  a  current  through 
the  sewage  between  poles  which  form  an  electrolyte  and  give  a 
nascent  oxygen  treatment  to  the  sewage.  In  addition  to  the  dis- 
infection, there  is  a  precipitation  of  a  part  of  the  suspended  matter. 


176 


SEWERS  AND  DRAINS 


Fig.  67.     General  View  of  Liquid  Chlorine  Disinfection  Plant 


r-i./  .Direction  of  Sewage  Flow  n 

Chlorine  Feed  Pipe^ — n          •  •-.  B 


^Diffusion  Chamber 


f_L          V     I  -  \SEWAQE  CHANNEL^ 
\  I      \}AdMe5h  Copper  frreeg* 


Wooden  Baffle^  j^Chlotipe  Feed   ^2  MY.  Pipe  I 
A 


Chlorinator       V__ 
CHEMICAL  HOU5E 


I— ' 


PL/IN 


Fig.  68.     Automatic  Chlorinator 


5ECTWN  /?-/? 

Fig.  69.     Plant  and  Sections  of  Disin- 
fection Plant 


SEWERS  AND  DRAINS 


177 


156.  Automatic  Appliances.     Automatic  devices  are  required 
for  efficient  disinfection  since  it  is  necessary  to  apply  the  solutions 
at  a  rate  in  proportion  to  the  flow  of  sewage,  and  as  the  flow  varies 
hourly.     With  the  use  of  chloride  of  lime,  this  can  be  accomplished 
by  a  float  chamber  connecting  to  the  sewer  and  arranged  so'  that 
the  float  operates  a  lever  which  varies  the  head  on  the  orifice  from 
the  solution  box  in  proportion  to  the  flow  of  sewage.     A  diaphragm 
control  from  a  Venturi  meter  on 

the  sewer  is  another  method. 
Liquid  chlorine  must  be  fed  by 
automatic  apparatus  that  not 
only  keeps  the  treatment  of  the 
sewage  uniform,  but  also  controls 
the  liquid  chlorine  pressure  tank. 

157.  Chlorine  Gas  Instalia= 
tion.  Figs.  67  to  69  show  a  typical 
installation  of  a  liquid-chlorine 
plant   for   treating   the  effluent 
from    a   sewage  disposal  plant. 
This  plant  consists   of   a  small 
brick  building,  Fig.  67,  in  which 
the  automatic  apparatus  is  lo- 
cated and  a  re-settling  basin  of 
reinforced   concrete   which    per- 
mits the  sewage  to  come  in  con- 
tact with  the  liquid  chlorine  for 
a  minimum  period  of  fifteen  min- 
utes before  being  discharged  into 
the    stream.     The   automatic 
apparatus,  Fig.  68,  is  controlled 
by    a    float    chamber,   Fig.   69, 

located  in  one  corner  of  the  pump  room  and  directly  con- 
nected to  the  sewer  outside  the  building  at  a  point  on  the  upstream 
side  of  a  fixed  weir.  This  float  transmits  the  difference  in  elevation, 
due  to  the  varying  flow  of  sewage  over  the  weir,  by  diaphragms 
directly  to  the  central  control  diaphragm.  Here  the  drop  in  pres- 
sure across  the  chlorine  gas  constriction  in  the  connecting  valve 
from  the  chlorine-pressure  tanks  is  kept  proportional  to  the  head 


Fig.  70.     Automatic  Contrbl  Apparatus  for 
Liquid  Chlorine 


178  SEWERS  AND  DRAINS 

on  the  weir.  This  gives  a  proportional  flow  of  chlorine  for  the 
varying  heads  over  the  weir.  The  liquid  chlorine  is  then  fed  to  the 
outfall  sewer  below  the  weir  and  is  liberated  in  a  baffled  concrete 
compartment  called  a  ''diffusion  chamber",  section  BE,  so  that 
the  chlorine  will  be  thoroughly  mixed  with  the  sewage  to  be  treated. 
Fig.  70  shows  another  type  of  liquid-chlorine  apparatus  where 
a  different  type  of  control  is  used.  This  consists  of  pressure  reg- 
ulating devices  to  produce  the  initial  cylinder  pressure  of  the  liquid 
chlorine  and  to  control  this  pressure  through  a  range  sufficient 
to  give  the  required  discharge  of  gas.  On  the  outlet  line,  there 
is  attached  a  low-pressure  chlorine  gauge  calibrated  to  indicate 
the  rate  of  flow  of  chlorine  gas.  This  apparatus  can  also  be  used 
in  connection  with  Venturi  meters  to  supply  the  chlorine  auto- 
matically in  proportion  to  the  flow  of  sewage. 

158.  Results.    Where  the  chlorine-gas  apparatus  is  used  on 
raw  sewage,  the  results  are  unreliable  if  there  are  large  pieces  of 
organic  matter  in  suspension,  as  the  treatment  will  not  destroy 
the  bacteria  inside  these  masses.     For  treatment  of  clarified  sewage 
or  effluents  from  disposal  works,  a  uniformly  high  degree  of  efficiency 
can  be  obtained. 

PUMPING 

159.  Requirements.    Where  it  is  at  all  possible  to  eliminate 
pumping,  it  should  be  avoided,  as  it  not  only  adds  a  high  operating 
cost,  but  also  is  difficult  in  maintenance.     Pumping  is,  however, 
a  necessity  at  many  disposal  works  where  the  outfall  sewer  is  too 
low  to  permit  of  gravity  operation  or  where  the  plant  would  other- 
wise be  subjected  to  flood  conditions.     It  is  necessary,  too,  for 
many  of  the  modern  buildings  in  our  large  cities  where  the  deep 
basements  and  sub-basements  are  entirely  too  low  to  drain  to  the 
sewers. 

160.  Method.     Sewage   pumps  must   be   reliable,   free   from 
obstructions,  and  in  many  cases  automatic.     Centrifugal  pumps 
with  open  type  impellers,  steam  or  motor  driven,  are  naturally 
adapted  to  sewage  pumping  on  account  of  simplicity,  possibility 
of  automatic  operation,  and  their  large  capacity  for  low  heads. 
Automatic  ejectors  operated  by  compressed  air  are  usually  used 
on  small  installations. 


SEWERS  AND  DRAINS  179 

161.  Design.     For  stations  that  are  to  be  automatic,  motor- 
driven  centrifugals  are  we'll  adapted.     The  pump  must  be  submerged 
and  preferably  placed  in  a  compartment  separate  from  the  sewage 
so  as  to  be  accessible  at  all  times.     Particular  attention  must  be 
paid  to  protecting  the  pumps  from  injury  or  clogging  from  suspended 
matter  in  the  raw  sewage,  and  for  this  purpose,  screen  chambers 
must  be  designed  and  installed  as  previously  outlined  under  that 
heading.     The  motor  should  be  placed  on  the  operating  floor  above 
the  pump  well  to  prevent  trouble  from  dampness. 

The  pump  well  must  be  of  capacity  sufficient  to  permit  the 
sewage  to  reach  the  pumps  without  swirling  and  also  to  give  some 
margin  for  a  temporary  closing  down  or  changing  over  of  pumps, 
and,  in  the  case  of  automatic  stations,  to  permit  of  proper  periods 
between  stopping  and  starting.  A  minimum  of  thirty  minutes' 
storage  of  the  maximum  flow  should  be  used.  In  determining 
the  size  of  the  pump,  study  must  be  made  of  the  varying  flow  of 
sewage  at  different  hours  of  the  day,  and  under  maximum  and  mini- 
mum conditions;  while  its  capacity  must  be  such  that  it  can  take 
care  of  the  flow  of  sewage  under  all  conditions  and  at  the  same  time 
permit  of  at  least  one  pumping  unit  being  out  of  operation.  Where 
there  is  a  possibility  of  the  supply  of  electric  current  being  inter- 
fered with,  auxiliary  power  should  be  provided. 

In  the  design  of  larger  stations  or  of  stations  where  the  cost 
of  current  is  not  comparable  with  other  fuel,  steam-driven  or  gas- 
engine-driven  installations  can  be  made,  but  stations  of  this  type 
must  be  supplied  with  operators. 

162.  Connellsville  Pumping  Station.     Fig.  71   shows  a  plan 
and  section  of  an  automatic  electric-driven  pumping  station  designed 
for  Connellsville,  Pennsylvania.     This  station  consists  of  a  circular 
pit  50  feet  in  diameter  by  30  feet  deep,  with  the  top  of  the  pit  carried 
up  to  the  natural  ground  level,  which  is  above  extreme  high-water 
mark,  and  with  the  bottom  of  the  pit  7  feet  below  the  invert  of 
the  connecting  sewer.     The  pumping  equipment  consists  of  two 
7-inch  centrifugal  pumps  run  by  electric  motors  and  each  having 
a  capacity  of  one  and  one-half  million  gallons  per  twenty-four 
hours;  and  one  10-inch  auxiliary  pump  run  by  a  gas  engine  and 
having  a  capacity  of  three  million  gallons  per  twenty-four  hours. 
There  is  a  concrete  diaphragm  wall  separating  the  pump  pit  from 


•Efectric^Motorond 
Pump  Vor Fresh 


-~  —  - T~  12" Drain  from 
3lud(je  Bed  No.l 

PLflM  and  SECTION  of  PUMP  HOUSE: 
Fig.  71.     Plan  and  Section  of  Connellsville  Proposed  Sewage  Pumping  Station 


SEWERS  AND  DRAINS  181 

the  suction  pit  so  that  the  pump  pit  will  be  dry  at  all  times  and 
pumps  can  be  conveniently  reached  for  inspection  or  repairs.  The 
main  suction  pit  will  have  an  effective  capacity  of  75,000  gallons 
or  a  minimum  storage  of  30  minutes  under  maximum  conditions. 
The  motors  operating  the  pumps  will  be  located  on  the  reinforced- 
concrete  operating  floor  above  the  pit  and  directly  connected  to 
the  pumps  by  vertical  steel  shafts.  Each  motor  will  be  automati- 
cally controlled  by  a  float  located  in  the  pit  and  connected  to  the 
switchboard  so  that  when  the  sewage  rises  in  the  pit  to  a  depth  of 
four  feet,  one  pump  starts  up.  If  the  flow  is  greater  than  the 
capacity  of  this  pump,  the  sewage  will  continue  to  rise  for  another 
foot  when  the  second  pump  will  start  up.  When  the  sewage  drops 
in  the  pit  to  within  two  feet  of  the  bottom,  the  last  pump  in  opera- 
tion is  cut  off  by  the  float  and  when  it  reaches  the  bottom,  the  second 
pump  is  placed  out  of  commission.  The  auxiliary  pump  is  provided 
to  take  care  of  any  breakdown  in  the  other  machinery  and  also 
to  provide  against  a  failure  of  the  current  supply.  A  small  3-inch 
pump  similar  to  the  other  electric-driven  pumps  is  provided  for 
taking  raw  water  from  the  river  and  supplying  it  for  flushing  pur- 
poses through  a  force  main  to  the  disposal  works. 

163.  Ejectors.  Figs.  72  and  73  show  an  installation  of  Shone 
ejectors  and  also  a  sectional  detail  of  one  of  these  ejectors.  Ejectors 
like  pumping  installations,  should  be  set  up  in  duplicate  as  indicated 
in  the  illustration,  so  that  there  will  be  a  spare  unit  for  use  in  emer- 
gency. Ejectors  are  simple  in  operation  as  they  have  no  working 
parts  which  can  become  clogged  with  suspended  matter,  and  when 
operated  with  compressed  air,  can  be  located  at  a  considerable 
distance  from  the  air  compressor  or  air  tank. 

As  will  be  noted  in  Fig.  73,  these  ejectors  consist  of  a  closed 
cast-iron  vessel  furnished  with  inlet  and  outlet  connections  which 
are  controlled  by  check  valves.  Gate  valves  are  also  provided, 
but  are  only  used  to  disconnect  one  unit  for  repairs.  On  top  of 
the  ejector  is  placed  an  automatic  valve  to  which  is  connected 
the  air  pipe  from  the  air  compressor.  This  valve  controls  the 
admission  of  the  compressed  air  into  the  ejector  and  also  the  exhaust 
of  displaced  air  from  the  ejector.  It  is  operated  by  the  two  cast- 
iron  bells  hung  in  reversed  positions  and  linked  to  each  other  by 
a  rod  through  the  center  of  the  main  compartment  as  shown.  When 


182 


SEWERS  AND  DRAINS 


SEWERS  AND  DRAINS 


183 


the  sewage  rises  in  the  ejector,  the  exhaust  valve  is  opened  and  the 
air  valve  is  closed,  the  bells  being  in  the  lower  position.  When  it 
reaches  the  top  of  the  ejector,  it  traps  air  in  the  upper  bell  forcing 
it  to  rise  by  buoyancy.  The  lever  connected  with  the  rod  from 
the  bells  quickly  closes  the  exhaust  and  opens  the  compressed-air 


AIREXHAUS 


INLET 
PIPE 


Fig.  73.     Detailed  Section  of  Shone  Automatic  Ejectors 

connection  and  the  compressed  air  immediately  forces  tne  sewage 
from  the  compartment  into  the  discharge  pipe.  Wlien  the  sewage 
reaches  the  lower  bell,  its  weight  pulls  down  the  control  rod,  thereby 
reversing  the  position  of  the  pressure  and  exhaust  valves  and  allow- 
ing the  ejector  to  start  again  the  process  of  filling.  It  requires 


184  SEWERS  AND  DRAINS 

very  little  more  air  pressure  to  operate  this  type  of  ejector  than 
the  head  of  water  against  which  it  must  lift. 

SUMMARY 

164.  Sewage=Disposal  Method — Question  of   Conditions.    It 

will  be  seen  from  the  outline  given  of  the  various  methods  of  sewage 
disposal  and  the  results  that  can  be  obtained,  that  each  case  must 
be  studied  and  worked  out  as  an  individual  problem.  Dilution 
is  feasible  under  certain  conditions,  but  usually  writh  some  treat- 
ment such  as  screening  or  disinfection,  or  a  partial  removal  of  the 
suspended  matters.  Broad  irrigation  and  chemical  precipitation, 
which  were  once  popular,  are  now  installed  only  under  exceptional 
conditions  on  account  of  the  high  cost  of  these  methods  of  treat- 
ment. A  non-putrescible  effluent  with  a  high  percentage  of  removal 
of  the  organic  matter  and  bacteria  can  be  obtained  by  broad  irriga- 
tion, but  only  a  partial  removal  of  it  can  be  obtained  by  chemical 
precipitation. 

1 65.  Care  of  Suspended  Matter  and  Effluent.     For  the  removal 
of  suspended  matters,  mechanical  screens,  Imhoff  tanks,  and  septic 
tanks  are  generally  used.     Where  there  is  danger  of  trouble  from 
odors,  screens  or  Imhoff  tanks  are  preferable.     Where  it  is  neces- 
sary to  produce  a  non-putrescible  effluent,  a  secondary  treatment 
must  be  given  the  effluent  from  which  the  suspended  matter  has 
been  removed,  and  this  is  accomplished  by  biological  filters  of 
which  the  sprinkling  filters  and  contact  beds  are  the  types  gener- 
ally used.     Sprinkling   filters   are   preferable  to  contact   beds  on 
account  of  lower  cost,  but  require  more  head  so  that  in  many  cases 
they  cannot  be  considered. 

166.  Disinfection  of  Effluent.     The  effluent  from  biological 
filters  is  not  free  from  bacteria  and  where  a  removal  of  pathogenic 
bacteria  is  required,   the   effluent   must   be   disinfected.     This  is 
generally  accomplished  by  chloride  of  lime  or  liquid  chlorine.     Sand 
filters  will  give  a  much  higher  degree  of  efficiency  than  the  coarse- 
grain  biological  filters,  but  on  account  of  high  cost  are  not  gener- 
ally used. 

Electrolytic  treatment  will  efficiently  disinfect  sewage,  but 
on  account  of  cost  of  treatment,  it  has  not  been  able  to  compete 
with  the  other  methods  of  disinfection.  Experiments  are  now 


SEWERS  AND  DRAINS  185 

being  conducted  on  activated  sludge,  formed  by  blowing  compressed 
air  through  freshly  deposited  suspended  matters.  This  process 
appears  to  liquefy  and  nitrify  the  sludge  in  a  very  short  period 
of  time  by  accelerating  the  growth  of  enormous  numbers  of  small 
worms  in  the  sludge  deposits.  These  experiments  indicate  a  develop- 
ment of  a  new  method  of  handling  the  sludge  problem,  although 
on  account  of  the  high  cost  of  operating  it  is  doubtful  whether  it 
will  be  as  economical  as  the  double-story  tank  method  with  separate 
digestion  compartment  now  so  generally  and  successfully  used. 

Pumping  should  be  avoided  if  possible.  If  it  must  be  used, 
the  apparatus  must  be  arranged  to  avoid  clogging  and  in  most  small 
installations  to  be  automatic.  Where  compressed  air  is  available, 
an  ejector  is  the  simplest  type  of  pump  to  use. 

167.  Future  Conditions.    As  the  population  of  this  country 
increases  and  new  towns  spring  up,  the  necessity  for  purification 
of  sewage  increases  and  the  time  is  not  far  off  when  even  our  sea- 
coast  cities  must  adopt  partial  purification.     It  is,  therefore,  of 
vital  importance  to  make  the  present  type  of  partial  treatment 
now  installed,  whatever  it  may  be,  subject  to  further  development 
of  a  higher  degree  of  purification. 

Finally,  too  much  emphasis  cannot  be  placed  on  the  importance 
of  a  thorough  study  of  conditions,  and  of  development  of  a  com- 
prehensive scheme  to  embrace  not  only  present  circumstances, 
but  future  contingencies. 

GARBAGE  DISPOSAL 

168.  Introduction.    The   disposal   of   garbage,    like   that   of 
sewage,  has  been  placed  on  a  scientific  basis  in  recent  years  only. 
Formerly,  it  was  common  practice  to  dump  it  into  rivers;  to  bury 
it  in  waste  tracts  of  land;  or  to  spread  it  on  these  tracts,  leaving 
it  to  rot  with  the  resultant  stench  and  nuisance.     In  recent  years, 
many  types  of  incinerators  and  reduction  plants  have  been  devel- 
oped and  placed  on  a  successful  operating  basis. 

169.  Composition  of  Garbage.    The  term  garbage  is  generally 
applied  to  the  rejected  food  wastes  of  a  community,  but  in  addition 
includes  ashes  and  household  rubbish,  as  well  as  street  sweepings, 
and  the  offal  from  slaughter  houses  and  carcasses.     The  average 
garbage  contains  70  per  cent  water,  3  per  cent  grease,  20  per  cent 


186  SEWERS  AND  DRAINS 

organic  matter,  while  the  balance  is  miscellaneous  material.  The 
household  wastes  consist  mainly  of  paper,  rags,  metal,  glass,  bottles, 
and  crockery.  Paper  and  rags  predominate  in  the  rubbish.  It 
has  been  estimated  by  Craven  that  in  the  New  York  City  rubbish, 
75  per  cent  is  paper  and  15.5  per  cent  rags. 

170.  Quantity.    The   amount   of   garbage   and*  other   waste 
materials  to  be  disposed  of  obviously  differs  greatly  in  different 
communities,    depending   to   a   great   extent   on   local   conditions. 
From  data  collected  in  several  cities  in  America,  it  is  found  that 
garbage  will  vary  from  100  to  200  pounds,  ashes  300  to  1000  pounds, 
and  rubbish  from  50  to  100  pounds,  per  capita  per  annum. 

171.  Disposal.     Household    garbage    has    a    food    value    for 
swine,  but  it  is  impossible  to  handle  it  in  a  sanitary  way  on  any 
great  scale  so  that  only  in  the  case  of  large  public  institutions,  or 
very  small  communities,  can  this  method  of  disposal  be  used.     The 
grease  and  organic  matter  also  have  a  commercial  value  for  soap 
and  fertilizer;  the  rubbish  can  be  sorted  and  sold,  but  as  in  the  case 
of  the  garbage,  there  is  no  economy  in  their  sale,  unless  it  be  carried 
to  a  considerable  extent.     The  ashes  are  valuable  for  filling  in 
low  tracts  of  land. 

For  towns  under  50,000  population,  the  best  method  for  dis- 
posing of  garbage  and  rubbish  is  by  incineration.  For  larger  cities, 
a  reduction  in  the  operating  cost  can  usually  be  effected  by  a  reduc- 
tion and  sorting  plant,  or  by  selling  it  to  a  reduction  company. 

172.  Collection.     Whatever    the    method    adopted,    dealing 
with  garbage,  it  is  preferable  to  collect  it  separately  from  the  rubbish 
and  ashes.     This  makes  the  handling  much  easier,  and  even  where 
all  materials  are  to  be  disposed  of  by  incineration,  permits  of  more 
efficient  charging  and  operation  of  the  incinerator.     The  garbage 
must  be  collected  in  water-tight  carts  with  air-tight  lids  and  arranged 
for  automatic  dumping  at  the  point  of  delivery.    The  other  material 
may  be  collected  in  ordinary  dump  wagons. 

INCINERATORS 

173.  Requirements.     The  essential  requirements  of  a  garbage 
incinerator  are:  (1)  economy  in  operation  with  freedom  from  odors; 
and  (2)  capacity  sufficient  to  take  care  of  the  entire  garbage  supply. 
It  is  necessary  first,  therefore,  to  know  the  character  and  amount 


SEWERS  AND  DRAINS  187 

of  material  to  be  taken  care  of.  It  is  obvious  that  to  burn  garbage 
only  will  require  a  design  of  furnace  radically  different  from  that 
used  to  burn  it  with  rubbish  or  ashes,  or  both.  Where  garbage 
alone  is  burned,  a  greater  amount  of  fuel  is  necessary,  while  drying 
grates  and  evaporating  pans  must  be  provided  to  prevent  the  liquids 
from  reaching  the  main  grate  bars.  After  determining  the  amount 
and  character  of  the  garbage  to  be  burned,  the  operating  periods 
must  be  determined.  A  continuous  operation  is  economical  from 
the  fuel  standpoint,  but  for  small  plants,  it  would  make  the  labor 
cost  too  high,  as  one  man  on  one  shift  can  easily  handle  eight  tons 
of  material. 

174.  Design.    The  design  of  garbage  crematories  has  been 
developed  by  a  great  number  of  companies,  and  the  patents  covering 
the  various  features  are  legion.     To  prevent  odors,  it  has  been 
found  that  a  temperature  of  1200°  F.  must  be  reached  in  the  gases 
in  the  outlet  flues  of  the  plant,  and  this  requirement,  together  with 
economy  of  fuel  consumption  and  permanence  of  grate  bars  and 
fire  linings,  is  the  controlling  feature.     A  good    furnace  builder 
could  design  an  incinerator  that  would  avoid  the  various  patents, 
but  it  is  doubtful  whether  this  design  would  also  incorporate  all 
of  the  desired  features  for  economy  and  permanence. 

It  is,  therefore,  better  for  the  engineer,  who  is  planning  to 
install  an  incinerator,  to  prepare  a  general  plan  and  specification 
for  the  work  and  to  permit  the  various  companies  to  submit  bids 
on  their  own  designs,  conforming  to  the  requirements  of  the  general 
plans  and  specifications.  Having  received  these  bids,  the  engineer 
should  carefully  study  the  various  features  of  each  design  and 
investigate  the  results  that  have  been  obtained  in  operation  with 
particular  attention  to  efficiency  and  replacement  charges.  A 
high  first  cost  is  in  many  cases  justified  by  the  saving  effected  in 
maintenance. 

REDUCTION  PLANTS 

175.  General  Conditions.    In  disposing  of  the  garbage  for 
cities  of  50,000  population  or  over,  a  considerable  saving  in  the 
operating  cost  can  be  effected  by  so  reducing  the  garbage  as  to 
obtain  the  fats  and  fertilizing  materials.     If  the  rubbish  is  collected 
separately,  it  will  also  pay  to  install  a  sorting  department. 


188  SEWERS  AND  DRAINS 

As  before  stated,  the  sorting  of  rubbish,  like  the  reduction  of 
garbage,  is  not  economical  unless  large  quantities  are  handled. 
The  waste  must  be  subdivided  into  a  great  many  parts  which 
requires  a  large  operating  force,  as  one  individual  can  handle  only 
two  or  three  parts.  The  sorting  is  usually  done  in  a  large  room; 
through  the  center  of  this  there  is  a  belt  conveyor,  along  which  are 
distributed  the  operating  force  who  pick  off  from  the  conveyor  the 
various  articles  to  be  sorted  as  they  pass. 

The  reduction  plants  are  in  most  cases  installed  and  operated 
by  a  private  company  which  makes  a  contract  with  the  city  for 
disposing  of  the  garbage.  There  are,  however,  several  municipal 
reduction  plants  which  have  been  installed  by  the  cities  and  oper- 
ated by  them  successfully. 

176.  Columbus  Reduction  Plant.  The  garbage  reduction 
plant  of  Columbus,  Ohio,  is  a  typical  one.  It  was  installed  by  the 
city  in  1910,  for  the  reduction  of  all  of  its  garbage.  The  plant  con- 
sists of  the  boiler  plant  and  machine  shop,  and  also  digesters,  presses, 
grease-separating  tanks,  percolators,  refining  and  storage  tanks, 
drying  equipment,  screens  and  evaporators.  The  garbage  is 
reduced  to  obtain  grease,  fertilizer,  and  hides,  the  last  of  course, 
being  stripped  before  the  carcasses  are  placed  in  the  reduction  plant 
proper. 

The  method  of  operation  consists  in  first  draining  off  the  liquids 
from  the  garbage  to  tanks;  here  the  grease  is  separated  by  gravity 
whence  it  is  pumped  to  treating  tanks.  After  the  grease  has  been 
removed,  the  water  is  pumped  to  an  evaporator  and  concentrated 
to  a  syrup  to  recover  the  solids  in  solution.  The  drained  garbage 
discharged  into  large  digesters  filled  with  steam  is  thoroughly  cooked. 
The  odors  or  gases  from  the  digesters  are  passed  through  condensers 
and  the  insoluble  gases  through  deodorizing  furnaces.  The  cooked 
garbage  is  next  subjected  to  presses  which  remove  the  solids  from 
the  liquids.  The  liquids  are  drawn  off  to  the  grease-separating 
room,  the  solids  being  carried  to  a  series  of  driers.  The  solids  are 
then  treated  in  sealed  containers  with  gasoline,  which  acts  as  a  sol- 
vent and  separates  what  grease  has  been  retained  in  them.  The 
gasoline  is  removed  by  means  of  dry  steam;  the  water,  grease,  and 
gasoline  are  separated  and  returned  to  their  respective  storage 
tanks.  The  solids  having  been  mixed  with  the  tankage  left  over 


SEWERS  AND  DRAINS  189 

from  the  evaporators  so  as  to  absorb  all  solids  contained  therein, 
are  now  dried  and  sold  for  fertilizer. 

The  operating  report  for  this  plant  in  1912,  showed  that  an 
average  of  60  tons  of  garbage  was  treated  per  day,  the  total  cost 
of  operation  of  the  plant  $38,500,  and  the  total  receipts  from  the 
products  $61,700.  As  the  plant  cost  $210,000,  it  is  necessary  to  add 
to  the  cost  of  operation  $15,500  for  interest  and  sinking  fund.  This 
leaves  a  balance  of  $7,700  profit.  The  above  outlined  cost  of 
operation  does  not,  however,  include  the  collection  of  the  garbage 
in  the  city  nor  its  delivery  to  the  disposal  works. 


INDEX. 


INDEX 


Alliance  filters 173 

Automatic  flushing  siphons 26 

Auxiliary  siphon 27 

Auxiliary  trap 26 

B 

Bell-holes 36 

Bell-mouth  arch 41 

Break  joints 42 

Brick 33 

Brick  masonry  in  sewers,  cost  of 102 

Brick  sewers r 41 

construction 129 

cost 99 

O 

Cast-iron  pipe 34 

Catch  basins 16 

Cement  sewer-pipe 33 

Cesspool 8 

Columbus  reduction  plant 188 

Concrete 33 

Concrete  sewers 42 

Connellsville  pumping  station__ 179 

Cross-sections  of  large  sewers 39 

Curing 38 

D 

Daily  fluctuation 65 

Drainage  ditches 83 

method  of  computing  sizes 89 

Drains 1 ,  83 

house  plumbing,  general  principles 95 

land 83 

large  ditches,  benefits 87 

subdrains 83 

tile ____83,  86 

Disconnecting  trap 95 

Disinfection 175 

automatic  appliances 177 

chlorine  gas  installation _  177 


2  INDEX 

PAGE 

Disinfection  (continued) 

method 175 

purpose 175 

results -__  178 

Dry  closet , , 9 

E 
Ejectors 181 

Engineering  and  contingencies 103 

F 

Flat  roofs 41 

Flush-tanks 16,  23 

Fresh-air  inlet 95 

G 

Garbage  disposal 185 

collection 186 

composition  of  garbage 185 

disposal 186 

introduction 185 

quantity ' 186 

Greenville  tanks ___ - 159 

H 

Hourly  fluctuation 65 

House  plumbing 95 

House  sewerage 93 

I 

Incinerators.  _1 186 

design 187 

requirements -  186 

Inverted  siphons 30 

J 
Junction-chambers  for  large  sewers 40 

L 

Lamp  holes T 16,23 

Land  drains 

Leaching  cesspool 

M 
Main  trap 26 

Manholes --16,  21,  103 

Manufacturing  sewage 

Miller  siphon 27 


INDEX  3 

PAGE 

o 

Open  drainage  ditches,  cost 93 

Outlets  for  sewer  systems 32 

P 

Pail  system  of  sewerage , 9 

Pipe  sewers 

cost 97 

joints  in 36 

Plumbers'  licenses 133 

Pneumatic  systems  of  sewerage 9 

Polk  filters 170 

Polk  tanks 152 

R 

Radial  flow  tanks 161 

Rangers 128 

Reduction  plants 187 

Columbus  reduction  plant 188 

general  conditions v 187 

Rhoads-Miller 27 

Roof  area _ . 76 

S       . 

Sand  filters 172 

alliance  filters 173 

design '_ 173 

use 172 

Sanitary  and  combined  sewers,  minimum  depths 18 

Sanitary  engineering 1 

Sanitary  sewage 1 

Sanitary  sewers 

ground  water  in i 66 

proper  capacities  of 66 

Seasonal  fluctuation . 65 

Septic  tanks 150 

Sewage  _  _  136 

analyses 136 

alkalinity  _  _  _  138 

bacteria 138 

chlorine 138 

nitrogen 137 

oxygen  consumed 138 

suspended  solids 137 

character ._ 136 

Sewage  disposal 33,  134 

basic  principle 134 

historical  _.  _   135 


4  INDEX 

PAGE 

Sewage  disposal  systems 140 

broad  irrigation 142 

efficiency 142 

general  principles 142 

chemical  precipitation 143 

efficiency 143 

conditions*  favoring 143 

controlling  factors 143 

classification  of  methods 140 

contact  beds 162 

alliance  filters 163 

basic  condition 162 

design 163 

head  required 166 

use 162 

dilution 140 

Chicago  sewage  __.      141 

controlling  factors 140 

examples 142 

disinfection 175 

Greenville  tanks. 159 

grit  chambers 148 

polk  tanks - 152 

pumping ---  178 

design _  179 

ejectors 181 

method 178 

requirements 178 

radial  flow  tanks 161 

requirements 140 

sand  filters  _ .                                                                                                 -  172 

screens 

coarse 144 

fine_- 

purpose -  144 

sedimentation  tanks 147 

classes 147 

efficiency -  147 

velocity -  148 

septic  tanks 150 

settling  tanks 

sludge -  150 

sprinkling  filters -  166 

two-story  tanks 155 

Sewer 

air " 2 

braces -  128 

brick 41 

gas 2 


INDEX  5 

PAGE 

Sewer  (continued) 

ordinances 132 

permits -  132 

profiles --108,  110 

reconnaissance -  105 

record  book . 130 

records -  132 

siphons 26 

tax 

warrants -  104 

Sewerage 

engineering 

map 110 

Sewerage  systems 7 

Berlier 9 

combined 10 

combined  and  separate,  comparative  merits 11 

crematory 9 

dry  closet 9 

Liernur 9 

pail 9 

preparation  of  plans  and  specifications 105 

separate 10 

water-carriage 10 

Sewer-pipe __34,  37 

Sewer  plans,  surveys 107 

bench  marks 108 

levels 108 

outlet  sewer 107 

sewage  disposal  site 107 

station  points 108 

street lp8 

Sewers 7,  13 

automatic  flushing  siphons 26 

brick '- 41 

calculation  of  maximum  percentage  of  run-off 79 

calculation  of  percentages  of  impervious  areas  on  sewer  watershed-.  76 

calculation  of  rate  of  rainfall  corresponding  to  time  of  concentration  __  75 

calculation  of  time  of  concentration 74 

calculations  of  sizes  and  minimum  grades  of  separate  sanitary  sewers.  _  58 

calculations  of  sizes  and  minimum  grades  of  storm  and  combined  sewers  71 
capacities  of  sanitary  sewers  required  'to  provide  for  fluctuations  in 

rate  of  flow 64 

cement  sewer-pipe 37 

concrete 42 

construction •_  _  125 

brick  sewers 129 

data J 130 

final  sewerage  map  and  profiles 131 


6  -     INDEX 

Sewers  (continued)  PAGE 

concrete 

laying  out  work 126 

letting  the  contract 125 

organization  of  engineering  force 126 

pipe  laying 129 

plat  of  sewer  connections  ___     131 

records 130 

sewer  record  book 130 

sheathing 128 

close 128 

skeleton 128 

trenching  and  refilling 127 

cost  and  methods  of  paying  for  them 96 

brick  sewers,  cost 99 

methods  of  paying 104 

pipe  sewers,  cost 97 

preliminary  estimates  of  cost 96 

cross-sections  of  large  sewers 39 

depth 18 

diagram  of  discharges  and  velocities  in  circular  sewers  at  different 

depths  of  flow 52 

diagram  of  discharges  and  velocities  in  egg-shaped  sewers  at  different 

depths  of  flow 54 

diagram  of  discharges  and  velocities  of  circular  brick  and  concrete 

sewers  flowing  full 47 

diagram  of  discharges  and  velocities  of  circular  pipe  sewers  flowing  full     45 
diagram  of  discharges  and  velocities  of  egg-shaped  brick  and  concrete 

sewers  flowing  full 49 

flush-tanks 23 

formulas  and  diagrams  for  computing  flow 43 

house  sewerage 93 

importance  and  value 5 

land  drains  and  subdrains 83 

maintenance  __> 132 

cleaning  of  catch  basins 134 

flushing  and  cleaning  of  sewers 133 

ordinances,  permits,  and  records 132 

plumbing  regulations,  tests,  licenses 132 

regular  sewer  inspection 133 

materials 

minimum  depths  for  sanitary  and  combined  sewers 18 

sewerage  systems 7 

specifications 

Sewers  and  drains -- 1-189 

drains 

historical  review 

general  description 

general  explanation  of  calculation  of  amount  of  sanitary  sewage 60 

general  explanation  of  calculation  of  amount  of  storm  sewage 72 


INDEX  7 

PAGE 

Sewers  and  drains  (continued) 

general  features 13 

ground  water  in  sanitary  sewers 66 

hand-flushing 

house  connections 20 

inverted  siphons.  __ 

junction-chambers  for  large  sewers 40 

kinds 13 

combined 

intercepting 

lateral 

main 14 

outlet 14 

storm 14 

sub-main 14 

lamp  holes.  __ 

location 16 

manholes 21 

materials 33 

brick. .                                            33 

cast-iron  pipe 34 

cement  sewer-pipe 33 

concrete 33 

stone 33 

wooden  stave  pipe 34 

methods  of  estimating  population  tributary  to  sanitary  sewers. 61 

minimum  grades  and  velocities  for  separate  sanitary  sewers 59 

minimum  sizes  of  sanitary  sewers 58 

outlets 32 

proper  capacities  of  sanitary  sewers 66 

street  inlets  and  catch  basins 29 

streets  vs.  alleys 17 

subdrains 19 

summary  of  laws  of  flow  in  sewers 57 

summary  of  methods  of  computing  sizes  of  separate  sanitary  sewers 67 

summary  of  methods  of  computing  sizes  of  storm  sewers 80 

table  of  sizes  required  for  sanitary  sewers 69 

use  of  sewer  gagings  in  determining   per  capita  flow  of  sanitary  sewage  64 
use  of  statistics  of  water  consumption  in  determining  per  capita  flow  of 

sanitary  sewage : 62 

ventilation 28 

vitrified  sewer-pipe  ___           34 

Sewers  and  sewage  disposal  plant,  specifications 112-125 

Sheet  piling 128 

Shove  joints 42 

Siphon-bell 26 

Sniff-hole  _ 27 

Soil  pipes 93,  95 

Sprinkling  filters _  166 


8  INDEX 

PAGE 

Sprinkling  filters  (continued) 

design 166 

examples 170 

Polk 170 

results — 170 

use 166 

Stone 33 

Storm  and  combined  sewers,  minimum  grades  and  velocities 71 

Storm  and  combined  sewers,  minimum  sizes 71 

Storm  sewage 2 

Street  inlets 16 

Street  sewer,  subdrain,  and  house  connection 16 

Subdrains 83 

Subdrains  for  sewers,  method  of  computing  sizes 89 

Tables 

approximate  percentages  of  impervious  area  in  cities 78 

composition  of  sewage  '__  136 

consumption  of  water  in  American  cities,  1895 63 

cost  of  tile  drains 92 

cubic  yards  per  linear  foot  of  brick  masonry  in  circular  sewers 101 

cubic  yards  per  linear  foot  of  brick  masonry  in  egg-shaped  sewers 101 

gagings  in  flow  of  sanitary  sewage 65 

minimum  grades  for  separate  sanitary  pipe  sewers 59 

minimum  grades  for  storm  and  combined  sewers 72 

number  of  acres  drained  by  open  ditches 90,  91 

number  of  acres  drained  by  tiles  removing  J^-inch  depth  of  water  in 

24  hours 88 

sizes  required  for  separate  sanitary  pipe  sewers 68 

standard  dimensions  for  sewer  pipe 36 

typical  analysis  of  city  sewage 137 

water  consumption  under  ordinary   conditions 64 

Tile  drains 83 

benefits 86 

contracts  and  specifications 84 

method    of    computing    sizes 88 

Tile  land  drains  and  drainage  ditches,  cost 92 

Traps 93,96 

Trenching  and  refilling 97 

Two-story  tanks 155 

V 

Vault  ribs 41 

Ventilation ---  96 

Venting 27 

Vitrified  sewer-pipe ---  34 

W 

Water  supply  engineering 

Wooden  stave  pipe 34 


GENERAL  LIBRARY 
UNIVERSITY  OF  CALIFORNIA—  BERKELEY 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

This  book  is  due  on  the  last  date  stamped  below,  or  on  the 
date  to  which  renewed. 


are  subject  to  immediate  recall. 


JAN  24  1955 

JRN2419551U 


21-100m-l,'54(1887sl8)476 


YC   13230 


/ffl 


UNJVERSJTYOFCAUFORNKUBRARV 


